Ultralow-iron-loss grain oriented silicon steel plate and process for producing the same

ABSTRACT

This invention can considerably improve the adhesion property of a film to a matrix surface of a silicon steel sheet by forming an interface layer such as nitride-oxide layer of one or more selected from Fe, Si, Al and B or an extremely thin base film formed by finely dispersing nitride-oxide of one or more selected from Fe, Si, Al and B in the same film components as a tension insulating film at an interface between the matrix surface and the tension insulating film, or further by immersing in an aqueous solution of a chloride mainly composed of SiCl 4  to dissolve the matrix surface or conducting a smoothening treatment or a pickling treatment with an aqueous solution containing SiCl 4  prior to the formation of the interface layer, and hence ultra-low core loss grain oriented silicon steel sheets having a core loss considerably superior to that of the conventional one and an excellent magnetostriction property can be obtained very cheaply and in a higher productivity.

TECHNICAL FIELD

This invention relates to a ultra-low core loss grain oriented siliconsteel sheet and a method of producing the same, and more particularlyits object it is to realize more improvement of core loss propertytogether with an improvement of compression stress in magnetostriction.

As will be detailed hereinafter, Applicants do this at low cost byforming an extremely thin Si-containing nitride-oxide layer on a surfaceof final annealed silicon steel sheet or a surface of final annealedsilicon steel sheet having a linear concave region and forming a tensioninsulating film thereon.

BACKGROUND ART

The grain oriented silicon steel sheet is mainly used as a core of atransformer or other electrical apparatus and is required to have a highmagnetic flux density (represented by B₈ value) and a low core loss(represented by W_(17/50)) as a magnetic property.

In order to improve the magnetic properties of the grain orientedsilicon steel sheet, it is required to highly align the <001> axis ofsecondary recrystallized grain in the steel sheet into the rollingdirection on one hand, and it is required to decrease impurities andprecipitates remaining in the final product as far as possible on theother hand.

For this end, after a basic production technique of the grain orientedsilicon steel sheet through two-stage cold rolling has been proposed byN. P. Goss, many improvements for such a production technique have beenrepeated to improve the magnetic flux density and core loss value of thegrain oriented silicon steel sheet every year.

Among them, there are typically a method described in JP-B-51-13469using Sb and MnSe or MnS as an inhibitor and a method described inJP-B-33-4710, JP-B-40-15644, JP-B-46-23820 and the like using AlN andMnS as an inhibitor. According to these methods, there was obtained aproduct having a high magnetic flux density that B₈ exceeds 1.88T.

In order to obtain a product having a higher magnetic flux density,JP-B-57-14737 discloses the composite addition of Mo to a startingmaterial or JP-B-62-42968 discloses the application of quenchingtreatment after the intermediate annealing just before final coldrolling after the composite addition of Mo to the starting material,whereby there are obtained a high magnetic flux density where B₈ is notless than 1.90T and a low core loss that core loss W_(17/50) is not morethan 1.05 W/kg (product thickness: 0.30 mm). However, there is left roomto be further improved as to sufficient reduction of core loss.

Particularly, it is considerably demanded to reduce power loss as far aspossible because of the energy crisis, and it is desired to more improvethe loss even in the application as an iron core material accompaniedtherewith. For this end, many products thinning the product thickness tonot more than 0.23 mm (9 mil) are used for decreasing eddy current lossas much as possible.

The aforementioned techniques are mainly metallurgical methods. Besidesthese methods, there is developed a method of reducing core loss(technique of finely dividing magnetic domain), in which the surface ofthe steel sheet after the final annealing is subjected to laserirradiation or plasma irradiation to artificially decrease the 180°magnetic domain width (B. Fukuda, K. Sato, T. Sugiyama, A. Honda and Y.Ito: Proc. of ASM Con. of Hard and Soft Magnetic Materials, 8710-008,(USA), (1987)). The core loss of the grain oriented silicon steel sheetis largely reduced by the development of such a technique.

However, this technique has a drawback that it is not durable toannealing at a higher temperature, so that there is a problem that theapplication is restricted to only a laminated core type transformer notrequiring strain relief annealing.

In this connection, a method wherein linear grooves are introduced in asurface of a steel sheet after the final annealing of the grain orientedsilicon steel sheet to finely divide magnetic domain throughanti-magnetic field effect of such grooves is industrialized as a finelymagnetic domain dividing technique durable to strain relief annealing(H. Kobayashi, E. Sasaki, M. Iwasaki and N. Takahashi: Proc. SMM-8.,(1987), P.402).

Besides this technique, a method wherein the magnetic domain is dividedby subjecting a final cold rolled sheet of the grain oriented siliconsteel sheet to a local electrolytic etching to form grooves(JP-B-8-6140) is also developed and industrialized.

Apart from the aforementioned production methods of the silicon steelsheet, amorphous alloys are noticed as a material for the usual powertransformer, high-frequency transformer or the like as disclosed inJP-B-55-19976, JP-A-56-127749 and JP-A-2-3213.

However, a very excellent core loss property is obtained in suchamorphous materials as compared with the conventional grain orientedsilicon steel sheet, but they have demerits in practical use becausethermal stability is lacking, space factor is poor, cutting is not easy,and they are too thin and brittle, to bringing about a large cost up inthe assembled step of the transformer, and hence it is not yet attainedto use a greater amount of such materials at the present time.

In addition, JP-B-52-24499 proposes a method wherein a forsterite basefilm formed after the final annealing of the silicon steel sheet isremoved and the surface of the steel sheet is polished and then thesurface of the steel sheet is subjected to a metal plating.

In this method, however, a low core loss is obtained at a lowtemperature, but when it is subjected to a high temperature treatment,the metal diffuses into the silicon steel sheet and there is a drawbackthat the core loss property is rather degraded.

In order to solve the above problem, the inventors have disclosed inJP-B-63-54767 and the like that an ultra-low core loss is obtained byforming one or more tension films selected from the group consisting ofnitrides and carbides of Si, Mn, Cr, Ni, Mo, W, V, Ti, Nb, Ta, Hf, Al,Cu, Zr and B on the grain oriented silicon steel sheet smoothened bypolishing through CVD or a dry plating (PVD) such as ion plating, ionimplantation or the like.

Although a very excellent core loss property as a material for a powertransformer, high-frequency transformer or the like is obtained by sucha production method, it can not be said to sufficiently respond to therecent demand for the attainment of low core loss.

Therefore, the inventors have made fundamental reexaminations from allviewpoints for more reducing the core loss as compared with theconventional one.

That is, in order to obtain product having a ultra-low core loss byforming one or more tension films selected from various nitrides andcarbides on the smoothened surface of the grain oriented silicon steelsheet at a stabilized step, the inventors became aware that it isrequired to conduct fundamental reexamination from raw materialcomponents of the grain oriented silicon steel sheet to the finaltreating step, and have made various studies from a pursuit on textureof a silicon steel sheet to smoothness of steel sheet surface or a finalCVD or PVD treating step.

As a result, we have found the following:

(1) A thin ceramic film covered on the silicon steel sheet (use TiN filmas a typical example) lessens the degree of improving the core loss evenwhen it is formed at a thickness of not less than 1.5 μm. That is, TiNfilm having a thickness of not less than 1.5 μm can expect a slightimprovement to the core loss and rather brings about the degradation ofspace factor and magnetic flux density.

(2) In this case, TiN is more important to play a role of adhesion tothe silicon steel sheet in addition to the application of tensioninherent to the ceramic. That is, when a lateral section of TiN isobserved by means of a transmission electron microscope (see YukioInokuti: Bulletin of The Japan Institute of Metals, 60(1996),P.781˜786), a lateral stripe of 10 nm is observed, which corresponds toa 5 atom layer of Fe—Fe atom in [011] direction of the silicon steelsheet.

(3) When a two-layer texture of a TiN covered zone and chemical polishedzone is simultaneously measured by X-ray (see Y Inokuti: ISIJInternational, 36(1996), P.347˜352), the {200} peak form of Fe in thepolished zone is an circle. However, the {200} peak form of Fe in theTiN covered zone is an ellipsoid and is at a state of strongly applyingtension in the [100]_(si-steel) direction of the silicon steel sheet.

(4) Tension of TiN film is 8˜10 MPa (see Yukio Inokuti, Kazuhiro Suzuki,Yasuhiro Kobayashi: Bulletin of The Japan Institute of Metals, 60(1996),P.674˜678), from which an improvement of magnetic flux density of about0.014˜0.016T can be expected. (This corresponds to the improvement ofdegree of Goss orientation alignment of about 1°).

Although the above is novel knowledge regarding the ceramic coating, wehave further obtained the following knowledge relating to surface stateof ceramic film and steel sheet.

(5) When the final cold rolled sheet of the silicon steel sheet issubjected to local electrolytic etching to form grooves and the surfaceof the steel sheet after the secondary recrystallization treatment issmoothened by polishing a TiN ceramic film is coated thereon, the coreloss is effectively reduced by fine division of magnetic domain throughthe anti-magnetic field that resulted from the formed grooves andfurther by the application of tension through the ceramic film.

(6) The effect of reducing the core loss by tension when a concavegroove is formed on the surface of the steel sheet prior to the ceramiccoating is larger than that of the silicon steel sheet smoothened by theusual polishing (see JP-B-3-32889).

That is, when the groove is formed, a difference between tension throughthe coating on the groove forming portion and tension through thecoating on the portion not forming the groove or a different tension isapplied to the surface of the silicon steel sheet to increase the degreeof reduction of the core loss by such a tension.

(7) When the ceramic film is coated on the silicon steel sheet havingthe concave grooves therein, the effect of reducing the core loss ismore effective than the case of smoothening by polishing and coating theceramic film.

That is, the linear grooves are formed to finely divide the magneticdomain through the anti-magnetic effect of these grooves and then theceramic tension film is formed to further finely divide 180° mainmagnetic domain, whereby ultra-low core loss is more effectivelyobtained.

(8) When the grooves are formed by subjecting the final cold rolledsheet of the silicon steel sheet to local electrolytic etching, even ifa TiN ceramic film is formed at a surface state that the surface of thesteel sheet after the secondary recrystallization treatment is notsmoothened by polishing, a considerable effect of reducing the core lossis developed. That is, when the ceramic film having a small thermalexpansion coefficient is coated even at a state of being not smoothenedby polishing, e.g. with small irregularities on the surface throughpickling treatment or the like, it is possible to apply a strong tensionto the surface of the silicon steel sheet, whereby the core loss canadvantageously be reduced.

We have made many experiments and examinations based on the aboveknowledge in order to achieve a given object and found out that it isvery effective to reduce the core loss when plural kinds of ceramictension films are formed on the surface of the silicon steel sheet ineither case of the surface-smoothened silicon steel sheet and the lineargroove-formed silicon steel sheet, and the thermal expansioncoefficients of these ceramic tension films are decreased toward theoutside, and grain oriented silicon steel sheets having a very low coreloss are newly developed (specification of Japanese Patent ApplicationNo. 9-328042).

The thus obtained grain oriented silicon steel sheets are provided witha very thin ceramic tension film having an excellent adhesion propertyand are possible to attain an ultra-low core loss and have an insulatingproperty and are excellent in the space factor, so that they arecertainly said to be ideal silicon steel sheets.

However, treatment in a high plasma atmosphere under vacuum isindispensable for forming such a dense ceramic film. In this case, theceramic film can not be formed at a high speed and productivity is low,so that there is a problem that the cost is up.

Besides this, Japanese Patent No. 2662482 and No. 2664326 recentlyproposed low core loss grain oriented silicon steel sheets havingimproved adhesion to film and core loss by forming a composite film ofoxidized Al-oxidized B on the smoothened surface of the steel sheet.

However, the core loss value W_(17/50) of the silicon steel sheet formedby these methods is only about 0.77˜0.83 W/kg in a product having athickness of 0.2 mm, so that it should be said that there is left roomto be improved because the core loss value is merely related to theextent the product thickness is thinned.

DISCLOSURE OF THE INVENTION

The inventors have made again investigations with respect to the surfacestate of the silicon steel sheet and further the tension insulating filmformed on the surface thereof based on the above knowledge.

And also, we have examined the improvement of compression stressproperty of magnetostriction (hereinafter referred to asmagnetostriction property simply).

The magnetostriction of the silicon steel sheet is a phenomenon ofelastically vibrating the steel sheet when the steel sheet ismagnetized, which is a greatest cause of noise in the transformer.

The magnetostriction behavior results from the fact that themagnetization course of the steel sheet includes 90° domain wallmovement and rotation magnetization, so that the magnetostrictionincreases in accordance with the compression stress applied to the steelsheet. In the assembling of the transformer, compression stress isinevitably applied to the steel sheet, so that the feature that tensionis previously applied to the steel sheet is advantageous in view ofcompression stress of magnetostriction. Of course, the application oftension to the steel sheet effectively contributes to improve the coreloss in the grain oriented silicon steel sheet.

Heretofore, it is attempted to improve the magnetostriction property inthe grain oriented silicon steel sheet by adding tension with sub-scale(SiO₂) formed on the surface of the steel sheet in decarburization andprimary recrystallization annealing prior to the secondaryrecrystallization, a forsterite base film formed by a high temperaturereaction in the final annealing with an annealing separator mainlycomposed of MgO and a tension insulating film formed thereon andconsisting essentially of phosphate and colloidal silica, but it can notbe expected to sufficiently improve the magnetostriction property to asatisfactory extent by such a conventional method.

As a result of the above investigations, it has been found that if aninterface layer including one or more nitride-oxide selected from Fe,Si, Al and B is formed on the surface of the silicon steel sheet, whenusual tension insulating film of a phosphate is subsequently formed as atension film, not only the core loss can considerably be reduced butalso the magnetostriction property can effectively be improved andfurther the improvement of production efficiency and reduction of thecost are attained.

That is, it has been discovered that it is effective to form anextremely thin Si-containing nitride-oxide layer on the surface of thesteel sheet by adhering one or more elements selected from Fe, Si, Aland B, particularly Si in an active state, and subsequently exposing toa non-oxidizing atmosphere containing N or subjecting it to a heattreatment in a non-oxidizing atmosphere.

And also, it has been found that when a treating solution obtained bydiluting a coating solution for the tension insulating film with waterprior to the formation of the tension insulating film consistingessentially of phosphate and colloidal silica and adding an inorganiccompound including one or more elements selected from Fe, Si, Al and Bto the diluted solution is applied thinly to adhere the inorganiccompound containing a slight amount of Fe or the like onto the surfaceof the steel sheet and thereafter preferably subjected to a heattreatment in a non-oxidizing atmosphere, an extremely thin film havingfundamentally the same film components as the tension insulating film isformed and also the inorganic compound existing in the film andincluding Fe or the like changes into a nitride-oxide of Fe or the likehaving a high activity to strongly adhere to the surface of the steelsheet and hence the extremely thin film is formed on the surface of thesteel sheet with a high adhesion. On the other hand, it has been foundthat since the extremely thin film is the same as the tension insulatingfilm formed thereon, the adhesion property of these films is very goodand hence the tension insulating film having a considerably excellentadhesion property as compared with the conventional one can be formed onthe surface of the steel sheet and as a result grain oriented siliconsteel sheets having a very low core loss and an excellentmagnetostriction property can be produced with high productivity and alow cost.

Further, it has been found that before the application of the treatingsolution obtained by adding a slight amount of an inorganic compoundsincluding one or more selected from Fe, Si, Al and B to a dilutedsolution of the coating solution consisting essentially of phosphate andcolloidal silica with water, when the grain oriented silicon steel sheetis immersed in an aqueous solution of SiCl₄ or a chloride consistingessentially of SiCl₄ to dissolve the surface of the matrix, or when asmoothening treatment or pickling treatment is carried out by using anaqueous solution containing SiCl₄, the adhesion property of the basefilm to the steel sheet is more improved.

The invention will concretely be described below.

Firstly, experimental results resulting in the invention are explained.

EXPERIMENT 1

A continuously cast slab of silicon steel having a composition of C:0.068 wt %, Si: 3.33 wt %, Mn: 0.067 wt %, Se: 0.020 wt %, Sb: 0.025 wt%, Al: 0.020 wt %, N: 0.0076 wt % and Mo: 0.013 wt % and the remainderbeing substantially Fe is heated at 1350° C. for 4 hours and hot rolledto obtain a hot rolled sheet of thickness: 2.0 mm. The hot rolled sheetis subjected to normalization annealing at 970° C. for 3 minutes androlled twice through an intermediate annealing at 1050° C. to obtain afinal cold rolled sheet of thickness: 0.23 mm.

Thereafter, the final cold rolled sheet is treated as follows.

{circle around (1)} An etching resist ink consisting essentially of analkyd resin is applied onto the surface of the final cold rolled sheetby gravure offset printing so as to leave linear non-coated portions ofwidth: 200 μm at an interval: 4 mm in a direction substantiallyperpendicular to a rolling direction, and baked at 200° C. for 3minutes. In this case, a resist thickness is 2 μm. The steel sheetcoated with the etching resist is subjected to an electrolytic etchingto form linear grooves of width: 200 μm and depth: 20 μm and thenimmersed in an organic solvent to remove the resist. In this case, theelectrolytic etching is carried out in NaCl electrolyte under conditionsof current density: 10 A/dm² and treating time: 20 seconds.

{circle around (2)} For the comparison, there is provided the final coldrolled sheet not subjected to the treatment of the item {circle around(1)}.

Thereafter, the steel sheets of the items {circle around (1)} and{circle around (2)} are subjected to decarburization and primaryrecrystallization annealing in wet H₂ of 840° C., and a slurry of anannealing separator having a composition of MgO(20%), Al₂O₃(75%) andCaSiO₃(5%) is applied to the surface of the steel sheet and annealed at850° C. for 15 hours and temperature is raised from 850° C. to 1150° C.at a rate of 10° C./h to develop secondary recrystallized grainsstrongly aligned in Goss orientation and subjected to purificationannealing in dry H₂ of 1200° C.

The surface film of the thus obtained product is removed and then thesurface of the silicon steel sheet is smoothened by chemical polishingand thereafter subjected to one of three treatments mentioned below.

(A) After an extremely thin Si film of about 0.02 μm in thickness isformed on the surface of the silicon steel sheet by magnetron sputteringprocess (one of PVD processes), it is treated in a mixed gas ofN₂(50%)+H₂(50%) at 1000° C. for 10 minutes. Thereafter, a tensioninsulating film (thickness of about 2 μm) consisting essentially ofcolloidal silica and phosphate is formed on the surface of the steelsheet and baked at 800° C.

(B) The surface of the silicon steel sheet is treated in a mixed gas ofSiCl₄+N₂+H₂ at 950° C. for 10 minutes (CVD process). Thereafter, atension insulating film (thickness of about 2 μm) consisting essentiallyof colloidal silica and phosphate is formed on the surface of the steelsheet and baked at 800° C.

(C) The silicon steel sheet is immersed in an aqueous solution of SiCl₄(0.5 mol/1) at 80° C. for 10 seconds and treated in a mixed gas ofN₂(50%)+H₂(50%) at 900° C. for 10 minutes. Thereafter, a tensioninsulating film (thickness of about 2 μm) consisting essentially ofcolloidal silica and phosphate is formed on the surface of the steelsheet and baked at 800° C.

The magnetic properties and adhesion property of the thus obtainedproducts and further analytical values of Si, O and N elements on thesurface of the silicon steel sheet prior to the formation of theinsulating film as measured by X-ray photoelectron microscopespectroscopic apparatus (X-ray Photoelectron Spectroscopy, XPS process)are shown in Table 1.

In Table 1 is also shown results when the surface of the grain orientedsilicon steel sheet is smoothened by chemical polishing after thesecondary recrystallization treatment is carried out by the methods{circle around (1)} and {circle around (2)} and the surface film isremoved from the product and then a tension insulating film (thicknessof about 2 μm) consisting essentially of colloidal silica and phosphateis formed on the surface of the steel sheet and baked at 800° C. as acomparative example.

TABLE 1 Formation of Magnetic extremely properties Adhesion propertiesXPS analysis Treating thin layer B₈ W_(17/50) bending (count/sec)condition containing Si (T) (W/kg) * evaluation Si N O {circle around(1)} A 1.91 0.59 20 mm ◯ 22000 1200  5100 {circle around (2)} 1.94 0.7220 mm ◯ — — — Comparative none 1.91 0.80 ** X  2000 280  800 of {circlearound (1)} {circle around (1)} B 1.90 0.60 20 mm ◯ — — — {circle around(2)} 1.94 0.73 30 mm ◯ 18000 1300  4200 Comparative none 1.93 0.93 ** X 1800 320  700 of {circle around (2)} {circle around (1)} C 1.91 0.59 20mm ◯ 13000 780 2300 {circle around (2)} 1.94 0.73 20 mm ◯ 12000 800 2200Comparative none 1.93 0.95 ** X  2900 330  900 of {circle around (2)}*Diameter (mm) causing no peeling of film by 180° bending on round rod.**Measurement of adhesion property is impossible due to the peeling offilm.

As seen from the results of Table 1, it is possible to produce ultra-lowcore loss grain oriented silicon steel sheets having excellent magneticproperties and adhesion property when the annealing treatment in thenon-oxidizing atmosphere is carried out after the formation of theextremely thin Si on the silicon steel sheet to form the Si-containingnitride-oxide layer on the surface of the silicon steel sheet (theincrease of Si, N, O is characteristic in the measurement of XPS, and agreat amount of O is observed in spite of the treatment in thenon-oxidizing atmosphere, and Si is easily bonded to oxygen) and thetension insulating film is formed thereon.

As mentioned above, when the PVD method (A) and the CVD method (B) areadopted as a method of forming Si film on the surface of the siliconsteel sheet, they cause the cost-up in the industrial production, butthe film thickness becomes extremely thin, so that the cost can bereduced by thinned portion as compared with the conventional method.

Particularly, the method (C) is noticed.

That is, the method (C) has a merit capable of conducting the treatmentvery cheaply and efficiently because it is enough to treat in the mixedgas of N₂(50%)+H₂(50%) at 900° C. for 10 minutes after the immersion inthe aqueous solution of SiCl₄ (0.5 mol/l) at 80° C. for 10 seconds.

As this type of the conventional technique, there is proposed a methodof forming an external oxidation type oxide layer of SiO₂ film on thepolished surface of the silicon steel sheet in JP-A-60-131976,JP-A-6-184762 and JP-A-9-78252.

However, the gist of these method is a method similar to the formationof sub-scale mainly composed of SiO₂ through the treatment in wet H₂ inthe decarburization-primary recrystallization annealing for removingharmful C in the silicon steel sheet. Particularly, in the method ofutilizing SiO₂ formed by such an oxidation treatment of the steel sheet,it has already been pointed out that the effect of reducing the coreloss through the mirror formation of the silicon steel sheet islessened.

And also, JP-A-5-279747 proposes a method of forming an insulating filmwherein an aqueous solution of lithium silicate (Li₂O.nSiO₂), sodiumsilicate (Na₂O.nSiO₂) or the like (water glass) is applied and baked asa base film prior to the application of an insulating coating consistingessentially of colloidal silica and phosphate on the surface of thegrain oriented electromagnetic steel sheet.

In this method, however, Si compound used as a material for the basefilm is an oxide form such as SiO₂, so that it is hardly said that theadhesion property to the surface of the steel sheet or the binder effectto the surface of the steel sheet is sufficient and hence there can notbe obtained the good adhesion property to the film and hence the effectof reducing the core loss as in the invention.

EXPERIMENT 2

A continuously cast slab of silicon steel having a composition of C:0.076 wt %, Si: 3.42 wt %, Mn: 0.075 wt %, Se: 0.020 wt %, Sb: 0.023 wt%, Al: 0.020 wt %, N: 0.0075 wt % and Mo: 0.012 wt % and the remainderbeing substantially Fe is heated at 1350° C. for 4 hours and hot rolledto obtain a hot rolled sheet of thickness: 2.0 mm. The hot rolled sheetis subjected to normalization annealing at 1000° C. for 3 minutes androlled twice through an intermediate annealing at 1020° C. to obtain afinal cold rolled sheet of thickness: 0.23 mm.

Thereafter, the final cold rolled sheet is treated as follows.

{circle around (1)} An etching resist ink consisting essentially of analkyd resin is applied onto the surface of the final cold rolled sheetby gravure offset printing so as to leave linear non-coated portions ofwidth: 200 μm at an interval: 4 mm in a direction substantiallyperpendicular to a rolling direction, and baked at 200° C. for 3minutes. In this case, a resist thickness is 2 μm. The steel sheetcoated with the etching resist is subjected to an electrolytic etchingto form linear grooves of width: 200 μm and depth: 20 μm and thenimmersed in an organic solvent to remove the resist. In this case, theelectrolytic etching is carried out in NaCl electrolyte under conditionsof current density: 10 A/dm² and treating time: 20 seconds.

{circle around (2)} For the comparison, there is provided the final coldrolled sheet not subjected to the treatment of the item {circle around(1)}.

Then, these steel sheets are subjected to decarburization and primaryrecrystallization annealing in wet H₂ of 840° C., and thereafter aslurry of an annealing separator having a composition of MgO(15%),Al₂O₃(75%) and CaSiO₃(10%) is applied to the surface of the steel sheet{circle around (1)}, while a slurry of an annealing separator mainlycomposed of MgO is applied to the surface of the steel sheet {circlearound (2)}, and then these sheets are annealed at 850° C. for 15 hoursand temperature is raised from 850° C. to 1150° C. at a rate of 10° C./hto develop secondary recrystallized grains strongly aligned in Gossorientation and subjected to purification annealing in dry H₂ of 1200°C.

Thereafter, the thus obtained steel sheets are subjected to thefollowing treatment.

(a) The oxide film on the surface of the silicon steel sheet treatedunder the condition {circle around (1)} is treated with a mixed picklingsolution of HCl(10%) and H₃PO₄(8%), immersed in an aqueous solution ofSiCl₄ (0.02 mol/l) at 85° C. for 30 seconds and then a tensioninsulating film (thickness of about 1.5 μm) consisting essentially ofmagnesium phosphate and colloidal silica is formed (800° C.) on thesurface of the steel sheet.

(b) After the oxide film on the surface of the silicon steel sheettreated under the condition {circle around (1)} is treated withHCl(10%), it is chemically polished with 3% hydrofluoric acid andhydrogen peroxide, immersed in an aqueous solution of SiCl₄ (0.02 mol/l)at 85° C. for 30 seconds and then a tension insulating film (thicknessof about 1.5 μm) consisting essentially of magnesium phosphate andcolloidal silica is formed (800° C.) on the surface of the steel sheet.

(c) On the surface of the silicon steel sheet provided with forsteritefilm treated under the condition {circle around (2)} is formed (800° C.)a tension insulating film (thickness of about 1.5 μm) consistingessentially of magnesium phosphate and colloidal silica.

The thus obtained silicon steel sheets are subjected to strain reliefannealing at 800° C. for 2 hours to obtain product sheets.

As the magnetic properties of each product sheet are measured, the sheet(a) has B₈=1.91T and W_(17/50)=0.66 W/kg and the sheet (b) has B₈=1.91Tand W_(17/50)=0.65 W/kg, which are very excellent as compared with theconventional sheet (c) having B₈=1.91T and W_(17/50)=0.73 W/kg.

And also, the compression stress property of magnetostriction in eachproduct sheet is measured to obtain results as shown in FIG. 1.

As shown in this figure, the increase of magnetic strain λ_(PP) ishardly observed in the invention examples (a) and (b) even whencompression stress is increased to 0.7 kg/mm², while in the conventionalsheet (c), the magnetic strain λ_(PP) rapidly increases when compressionstress is not less than 0.35 kg/mm², and the magnetic strain λ_(PP)indicates a large value reaching to 3.2×10⁻⁶ when compression stress is0.50 kg/mm².

The reason why the compression stress property of magnetostriction isimproved by forming an extremely thin Si-containing nitride-oxide layerprior to the formation of the tension insulating film according to theinvention is considered as follows.

That is, in the existing silicon steel sheet having forsterite basefilm, as shown in FIG. 2(a), many anchors made of sulfide or nitride areexistent just beneath the surface of the steel sheet (about 2˜3 μm), sothat the movement of magnetic domain is obstructed. When the forsteritebase film of the silicon steel sheet is formed by solid phase reactionbetween MgO and the sub-scale (SiO₂) on the surface of the silicon steelsheet in the secondary recrystallization annealing in Goss orientation,the adhesion property to the matrix is ensured by the presence of manyanchors as mentioned above. For this end, the magnetic strain λ_(PP) ofthe silicon steel sheet increases as compression stress is applied.

On the contrary, in the silicon steel sheet strongly adhered with theinsulating film through the strong binder effect of the extremely thinSi-containing nitride-oxide layer formed on the matrix surface accordingto the invention, the movement of magnetic domain is easy and alsotension is directly applied to the steel sheet, so that the compressionstress property of magnetostriction is effectively improved.

Moreover, it goes without saying that tensile stress applied to such asilicon steel sheet is effective to improve not only themagnetostriction but also the core loss, and particularly the effectthereof is conspicuous in case of the grain oriented silicon steel sheethaving a high magnetic flux density highly aligned in Goss orientation.

EXPERIMENT 3

A continuously cast slab of silicon steel having a composition of C:0.067 wt %, Si: 3.38 wt %, Mn: 0.077 wt %, Se: 0.020 wt %, Sb: 0.023 wt%, Al: 0.021 wt %, N: 0.0078 wt % and Mo: 0.012 wt % and the remainderbeing substantially Fe is heated at 1340° C. for 5 hours and hot rolledto obtain a hot rolled sheet of thickness: 2.0 mm. The hot rolled sheetis subjected to normalization annealing at 980° C. for 3 minutes androlled twice through an intermediate annealing at 1030° C. to obtain afinal cold rolled sheet of thickness: 0.23 mm.

Thereafter, the final cold rolled sheet is treated as follows.

{circle around (1)} An etching resist ink consisting essentially of analkyd resin is applied onto the surface of the final cold rolled sheetby gravure offset printing so as to leave linear non-coated portions ofwidth: 200 μm at an interval: 4 mm in a direction substantiallyperpendicular to a rolling direction, and baked at 200° C. for 3minutes. In this case, a resist thickness is 2 μm. The steel sheetcoated with the etching resist is subjected to an electrolytic etchingto form linear grooves of width: 200 μm and depth: 20 μm and thenimmersed in an organic solvent to remove the resist. In this case, theelectrolytic etching is carried out in NaCl electrolyte under conditionsof current density: 10 A/dm² and treating time: 20 seconds.

{circle around (2)} For the comparison, there is provided the final coldrolled sheet not subjected to the treatment of the item {circle around(1)}.

Thereafter, the steel sheets of the items {circle around (1)} and{circle around (2)} are subjected to decarburization and primaryrecrystallization annealing in wet H₂ of 840° C., and a slurry of anannealing separator having a composition of MgO(15%), Al₂O₃(75%) andCaSiO₃(10%) is applied to the surface of the steel sheet and annealed at850° C. for 15 hours and temperature is raised from 850° C. to 1150° C.at a rate of 12° C./h to develop secondary recrystallized grainsstrongly aligned in Goss orientation and subjected to purificationannealing in dry H₂ of 1220° C.

The surface film of the thus obtained product is removed and then thesurface of the silicon steel sheet is smoothened by chemical polishingand thereafter subjected to one of six treatments mentioned below.

(A) The silicon steel sheet is immersed in a treating solution of 80° C.obtained by diluting 250 cc of a coating solution for tension insulatingfilm consisting essentially of phosphate and colloidal silica with 1500cc of distilled water and further adding 25 cc of SiCl₄ solution to thediluted solution for 20 seconds, washed with water and dried.

(B) The silicon steel sheet is immersed in a treating solution of 80° C.obtained by diluting 250 cc of a coating solution for tension insulatingfilm consisting essentially of phosphate and colloidal silica with 1500cc of distilled water and further adding 25 cc of SiCl₄ solution and 25g of FeCl₃ together to the diluted solution for 20 seconds, washed withwater and dried.

(C) The silicon steel sheet is immersed in a treating solution of 80° C.obtained by diluting 250 cc of a coating solution for tension insulatingfilm consisting essentially of phosphate and colloidal silica with 1500cc of distilled water and further adding 25 cc of SiCl₄ solution and 25g of AlPO₄.3/2H₂O together to the diluted solution for 20 seconds,washed with water and dried.

(D) The silicon steel sheet is immersed in a treating solution of 80° C.obtained by diluting 250 cc of a coating solution for tension insulatingfilm consisting essentially of phosphate and colloidal silica with 1500cc of distilled water and further adding 20 g of FeCl₃, 20 g of Al(NO₃)and 10 g of H₃BO₃ together to the diluted solution for 20 seconds,washed with water and dried.

(E) The silicon steel sheet is immersed in a treating solution of 80° C.obtained by diluting 250 cc of a coating solution for tension insulatingfilm consisting essentially of phosphate and colloidal silica with 1500cc of distilled water for 20 seconds, washed with water and dried.

(F) The silicon steel sheet is immersed in a treating solution of 80° C.obtained by diluting 250 cc of a coating solution for tension insulatingfilm consisting essentially of phosphate and colloidal silica with 1500cc of distilled water and further adding 25 cc of SiCl₄ solution to thediluted solution for 20 seconds, washed with water and dried.

(G) After the final annealing, the oxide on the surface of the siliconsteel sheet is removed by pickling.

Then, the silicon steel sheets treated in the items (A)˜(E) aresubjected to a heat treatment in a mixed gas of N₂(50%)+H₂(50%) at 950°C. for 10 minutes.

Thereafter, a tension insulating film (thickness of about 2 μm)consisting essentially of magnesium phosphate and colloidal silica isformed (800° C.) on the surface of the steel sheet.

The magnetic properties and adhesion property of the thus obtainedproducts are measured to obtain results as shown in Table 2.

TABLE 2 Magnetic Treating method properties Adhesion (solutionconsisting essentially of B₈ W_(17/50) property* Condition phosphate andcolloidal silica) (T) (W/kg) (mm) Remarks {circle around (1)}-A SiCl₄:50 cc 1.90 0.58 20 Invention Example {circle around (1)}-B SiCl₄: 25 ccand FeCl₂: 25 g 1.91 0.57 25 Invention Example {circle around (1)}-CSiCl₄: 25 cc and AlPO₄: 25 g 1.90 0.59 20 Invention Example {circlearound (1)}-D FeCl₃: 20 g, Al(NO₃)₃: 20 g and 1.91 0.59 20 InventionH₃BO₃: 10 g Example {circle around (1)}-E no addition of inorganiccompound 1.90 0.72 X Comparative including Si, Fe, Al, B (peeling)Example {circle around (1)}-F SiCl₄: 50 cc 1.90 0.60 25 Invention noannealing of (H₂ + N₂) at 950° C. Example {circle around (1)}-G grainoriented silicon steel sheet not 1.88 0.77 X Comparative subjected tochemical polishing (peeling) Example treatment or the like {circlearound (2)}-H grain oriented silicon steel sheet not 1.93 0.88 30Comparative subjected to groove-forming Example treatment *Diameter (mm)causing no peeling by 180° bending.

As seen from the results of Table 2, in the invention examples of{circle around (1)}-A˜{circle around (1)}-D, i.e. the cases wherein thesilicon steel sheet having a surface smoothened by chemical polishingsurface is immersed in the treating solution obtained by diluting thecoating solution for tension insulating film consisting essentially ofphosphate and colloidal silica with the diluted water and adding aslight amount of the inorganic compound including Fe, Si, Al, B and thelike, subjected to an annealing treatment in a non-oxidizing atmosphereto form an extremely thin base film formed by finely dispersing one ormore nitride-oxide selected from Fe, Si, Al and B into components fortension insulating film on the surface of the steel sheet and thetension insulating film consisting essentially of phosphate andcolloidal silica is formed according to usual manner, there can beobtained ultra-low core loss that the core loss is not more than 0.6W/kg and an excellent adhesion property that the diameter causing nopeeling by 180° bending is not more than 15 mm.

Even in the case {circle around (1)}-F wherein the diluted solution ofthe coating solution for tension insulating film added with a slightamount of the inorganic compound including Fe, Si, Al, B is applied andthe tension insulating film consisting essentially of phosphate andcolloidal silica is formed immediately according to usual manner withthe omission of the subsequent annealing treatment, there can beobtained excellent core loss property and adhesion property to the filmequal to those of the cases {circle around (1)}-A˜{circle around (1)}-D.

On the contrary, in the case {circle around (1)}-F wherein the dilutedsolution of the coating solution for tension insulating film not addedwith a slight amount of the inorganic compound including Fe, Si, Al, Bis merely used as the treating solution for the base film, the effect ofimproving the core loss is observed by the smoothening treatment throughthe chemical polishing, but the adhesion property is very poor and thepeeling is rapidly caused in the bending test, so that it can not beused as the silicon steel sheet.

And also, in the case {circle around (1)}-G wherein the chemicalpolishing and subsequent formation of the extremely thin base film arenot carried out, the improvement of the core loss is carried out only bythe fine division of magnetic domain, so that the core loss level of thesilicon steel sheet is fairly poor as compared with that of theinvention.

In FIG. 3 is shown the film structure of the grain oriented siliconsteel sheet according to the invention (FIG. 3(c)) in comparison withthose of the conventional grain oriented silicon steel sheets (FIGS.3(a), (b)).

FIG. 3(a) is a case that the tension insulating film consistingessentially of phosphate and colloidal silica is merely formed on thesurface of the grain oriented silicon steel sheet after the finalannealing as disclosed in JP-A-5-311353. In this case, the adhesionproperty between the silicon steel sheet and the insulating film comesinto a great problem, so that it is difficult to use as a practicalproduct.

And also, FIG. 3(b) is a case that an extremely thin ceramic film ofTiN, CrN or the like is formed on the surface of the grain orientedsilicon steel sheet smoothened by polishing through CVD or PVD and thena tension insulating film is formed thereon as disclosed inJP-B-63-35686. This is very effective to reduce the core loss, but theplasma treatment under high vacuum is required as previously mentioned,so that it is disadvantageous to bring about the cost-up.

On the contrary, in the invention example of FIG. 3(c), the extremelythin base film finely dispersed with a slight amount of nitride-oxide ofFe, Si, Al and B is formed on the interface between the grain orientedsilicon steel sheet and the tension insulating film, so that theadhesion property to the silicon steel sheet is considerably improvedand hence it is considered that the application of tension by thetension insulating film is effectively conducted.

That is, according to the invention, nitride-oxide of Fe, Si, Al and Bis finely dispersed into the extremely thin base film to strongly adherethe base film to the matrix of the silicon steel, while since the maincomponents of the base film are the same as the tension insulating filmformed thereon, the adhesion property between the base film and theupper tension insulating film is good and hence the tension applyingfunction of the upper tension insulating film can sufficiently bedeveloped by interposing the base film to attain the effect of moreimproving the core loss.

Therefore, it can be said that the extremely thin base film is good inthe adhesion property to the matrix of the silicon steel sheet and theadhesion property to the tension insulating film and is a filmpossessing an action of a binder between the matrix of the silicon steelsheet and the tension insulating film.

As the extremely thin base film, it is important that such a filmcontains Fe, Si, Al, B and the like the form of nitride-oxide. For thisend, it is important to use a diluted solution obtained by diluting theusual coating solution for tension insulating film with water so as tofacilitate the inorganic compound including Fe, Si, Al and B as astarting material to nitride-oxide as the treating solution, and also itis important to make the thickness of the film as thin as possible whilesatisfying the necessary thickness.

When the coating solution for tension insulating film is diluted asmentioned above, the feature that the inorganic compound of Fe, Si, Aland B included in the diluted solution is easily converted intonitride-oxide by the subsequent heat treatment is shown in Table 3.

Table 3 shows analytical values of Fe, Si, N, O on the surface of thesilicon steel sheet prior to the formation of the tension insulatingfilm as measured by X-ray photoelectron microscope spectroscopicapparatus (X-ray Photoelectron Spectroscopy, XPS process). As shown inthis table, a great amount of Fe, N, O is observed in the inventionexample, and particularly a great amount of O is observed in spite ofthe treatment in the non-oxidizing atmosphere, which shows that Feeasily bonds to oxygen. And also, Si somewhat increases, which isconsidered due to the fact that colloidal silica in the base film isincorporated.

TABLE 3 Treating method (solution consisting essentially of phosphateXPS process (cps) Condition and colloidal silica) Fe Si N O Remarks{circle around (1)}-A SiCl₄: 50 cc 1600 7000 800 1500 Invention Example{circle around (1)}-B SiCl₄: 25 cc, FeCl₃: 25 g 3900 6500 760 1550Invention Example {circle around (1)}-E no addition of inorganic 13005500 300  890 Comparative compound including Si, Example Fe, Al, B

Further, FIG. 4 shows results of oxide composition in the nitride-oxideas measured by XPS process when the extremely thin base film dispersedwith nitride-oxide of Si is formed on the surface of the steel sheet byutilizing SiCl₄ as an inorganic compound of Fe, Si, Al, B and the like.

As seen from this figure, the oxide formed by this method is noticed tobe mainly composed of FeSiO₃ (Clinoferrosilite) and Fe₂SiO₄ (Fayalite)(Moreover, the amount of FeSiO₃ produced is larger than that of Fe₂SiO₄,strictly speaking).

In this case, the above oxide is considered to be formed by the reactionof the following equation:

SiCl₄+2H₂O+2FeO→Fe₂SiO₄+4HCl

And also, the above oxide is very dense different from the conventionalSiO₂ sub-scale and such a dense oxide produces together with finenitride, so that it is considered to considerably improve the adhesionproperty as compared with the conventional one.

EXPERIMENT 4

A continuously cast slab of silicon steel having a composition of C:0.073 wt %, Si: 3.38 wt %, Mn: 0.070 wt %, Se: 0.020 wt %, Sb: 0.025 wt%, Al: 0.020 wt %, N: 0.0078 wt % and Mo: 0.012 wt % and the remainderbeing substantially Fe is heated at 1340° C. for 5 hours and hot rolledto obtain a hot rolled sheet of thickness: 2.0 mm. The hot rolled sheetis subjected to normalization annealing at 1000° C. for 3 minutes androlled twice through an intermediate annealing at 1050° C. to obtain afinal cold rolled sheet of thickness: 0.23 mm.

Thereafter, the final cold rolled sheet is treated as follows.

An etching resist ink consisting essentially of an alkyd resin isapplied onto the surface of the final cold rolled sheet by gravureoffset printing so as to leave linear non-coated portions of width: 200μm at an interval: 4 mm in a direction substantially perpendicular to arolling direction, and baked at 200° C. for 3 minutes. In this case, aresist thickness is 2 μm. The steel sheet coated with the etching resistis subjected to an electrolytic etching to form linear grooves of width:200 μm and depth: 20 μm and then immersed in an organic solvent toremove the resist. In this case, the electrolytic etching is carried outin NaCl electrolyte under conditions of current density: 10 A/dm² andtreating time: 20 seconds.

Thereafter, the steel sheet is subjected to decarburization and primaryrecrystallization annealing in wet H₂ of 840° C., and a slurry of anannealing separator having a composition of CaO(20%), Al₂O₃(60%) andSiO₂(20%) is applied to the surface of the steel sheet and annealed at850° C. for 15 hours and temperature is raised from 850° C. to 1150° C.at a rate of 10° C./h to develop secondary recrystallized grainsstrongly aligned in Goss orientation and subjected to purificationannealing in dry H₂ of 1220° C.

The surface film of the thus obtained product is removed and then thesurface of the silicon steel sheet is smoothened by chemical polishingand thereafter subjected to a treatment at a step mentioned below.

(A) Step

The silicon steel sheet is immersed in an aqueous solution of SiCl₄solution: 20 cc dissolved in 1500 cc of a distilled water at 80° C. for1˜90 seconds, and further immersed in a treating solution of 80° C.formed by adding SiCl₄ solution: 30 cc, AlPO₄: 20 g and H₃PO₃: 20 gtogether to a diluted solution formed by diluting a coating solution fortension insulating film consisting essentially of phosphate andcolloidal silica: 250 cc with 1500 cc of a distilled water for 1˜60seconds, washed with water and dried.

(B) Step

The silicon steel sheet is immersed in an aqueous solution of SiCl₄solution: 30 cc dissolved in 1500 cc of a distilled water at 80° C. for1˜90 seconds, and further immersed in a treating solution of 80° C.formed by adding SiCl₄ solution: 30 cc, AlPO₄: 20 g and H₃PO₃: 20 gtogether to a diluted solution formed by diluting a coating solution fortension insulating film consisting essentially of phosphate andcolloidal silica: 250 cc with 2000 cc of a distilled water for 1˜60seconds, washed with water and dried.

(C) Step

The silicon steel sheet is immersed in an aqueous solution of SiCl₄solution: 20 cc and FeCl₃: 10 g dissolved in 1500 cc of a distilledwater at 80° C. for 1˜90 seconds, and further immersed in a treatingsolution of 80° C. formed by adding SiCl₄ solution: 25 cc, FeCl₃: 15 g,AlPO₄: 10 g and H₃PO₃: 10 g together to a diluted solution formed bydiluting a coating solution for tension insulating film consistingessentially of phosphate and colloidal silica: 250 cc with 1500 cc of adistilled water for 1˜90 seconds, washed with water and dried.

Thereafter, the silicon steel sheets treated in the (A)˜(C) steps aretreated in a mixed gas of N₂(50%)+H₂(50%) at 950° C. for 10 minutes,respectively.

Then, a coating solution for tension insulating film consistingessentially of phosphate and colloidal silica is applied onto thesurface of the thus obtained steel sheet, dried and baked in N₂ gas at800° C. to form a tension insulating film having a thickness of 2.0 μm.

A relation between core loss property W_(17/50) (W/kg) of each of thethus obtained products and amount of sheet thickness decreased (bothsurfaces) before the application of the coating solution for tensioninsulating film is examined to obtain results as shown in FIG. 5.

As seen from this figure, the effect of reducing the core loss W17/50(W/kg) of the silicon steel sheet is conspicuous when the decreasedamount of sheet thickness is within a range of 0.01˜3.0 μm in all of the(A), (B) and (C) steps.

This reason is considered as follows.

That is, the silicon steel sheet is immersed in an aqueous solution ofSiCl₄ or a chloride mainly composed of SiCl₄ prior to the formation ofthe base film to promote the surface reaction of the steel sheet todissolve Fe component on the surface of the steel sheet to a certainextent, whereby the activity and hence the adhesion property of thesteel sheet surface are enhanced. Then, fine nitride-oxide of Fe, Si,Al, B and the like in the base film strongly adheres to the activatedsurface of the steel sheet, and such nitride-oxide serves as an anchorto improve the adhesion property between the silicon steel sheet and thebase film and at the same time improve the tension applying effectthrough the tension insulating film formed thereon, whereby it isconsidered to obtain the ultra-low core loss.

The state of the interface between the above silicon steel sheet and thebase film is considered to create a phenomenon similar to the lateralstripes of about 10 nm observed in the interface of the TiN coatedsilicon steel sheet of the above item (2) as observed by an electronmicroscope.

In the invention, it is theoretically impossible to create the thininterface layer approximately equal to TiN formed by plasma treatmentunder vacuum of PVD, but it is noticed that the ultra-low core loss ofthe grain oriented silicon steel sheet can be attained by activating thesurface of the steel sheet cheaply without using such a vacuum plasmaprocess.

And also, the decrease of the sheet thickness of 0.01˜3.0 μm with thechloride solution in the above silicon steel sheet corresponds to aweight reduction of 0.0005˜0.15 g.

Namely, in case of the plasma in the vacuum treatment, it is possible tocreate a just ideal mixed layer by creating the phenomenon similar tothe lateral stripe of about 10 nm observed in the interface of the TiNcoated silicon steel sheet of the above item (2) by an electronmicroscope, but the surface of the steel sheet is activated by creatingthe weight reduction of 0.0005˜0.15 g in the silicon steel sheet withoutusing the vacuum as in the invention, whereby the fine nitride-oxide ofFe, Si, Al, B and the like is preferentially formed in the interfacelayer to attain the ultra-low core loss.

EXPERIMENT 5

A continuously cast slab of silicon steel having a composition of C:0.069 wt %, Si: 3.42 wt %, Mn: 0.075 wt %, Se: 0.020 wt %, Sb: 0.025 wt%, Al: 0.020 wt %, N: 0.0073 wt % and Mo: 0.012 wt % and the remainderbeing substantially Fe is heated at 1360° C. for 5 hours and hot rolledto obtain a hot rolled sheet of thickness: 2.0 mm. The hot rolled sheetis subjected to normalization annealing at 1020° C. for 3 minutes androlled twice through an intermediate annealing at 1050° C. to obtain afinal cold rolled sheet of thickness: 0.23 mm.

Thereafter, the final cold rolled sheet is treated as follows.

An etching resist ink consisting essentially of an alkyd resin isapplied onto the surface of the final cold rolled sheet by gravureoffset printing so as to leave linear non-coated portions of width: 200μm at an interval: 4 mm in a direction substantially perpendicular to arolling direction, and baked at 200° C. for 3 minutes. In this case, aresist thickness is 2 μm. The steel sheet coated with the etching resistis subjected to an electrolytic etching to form linear grooves of width:200 μm and depth: 20 μm and then immersed in an organic solvent toremove the resist. In this case, the electrolytic etching is carried outin NaCl electrolyte under conditions of current density: 10 A/dm² andtreating time: 20 seconds.

Thereafter, the steel sheet is subjected to decarburization and primaryrecrystallization annealing in wet H₂ of 840° C., and a slurry of anannealing separator having a composition of CaO(20%), Al₂O₃(50%) andSiO₂(30%) is applied to the surface of the steel sheet and annealed at850° C. for 15 hours and temperature is raised from 850° C. to 1150° C.at a rate of 12° C./h to develop secondary recrystallized grainsstrongly aligned in Goss orientation and subjected to purificationannealing in dry H₂ of 1200° C.

The surface of the thus obtained silicon steel sheet having noforsterite film is treated at a step mentioned below.

(A) Step

The oxide on the surface of the steel sheet is removed by immersing inan aqueous solution (80° C.) of SiCl₄: 30 cc in 1500 cc of a distilledwater for 1 minute.

(B) Step

The oxide on the surface of the steel sheet is removed by immersing inan aqueous solution (80° C.) of SiCl₄: 20 cc and HCl: 20 cc in 1500 ccof a distilled water for 1 minute.

(C) Step

The oxide on the surface of the steel sheet is removed by immersing inan aqueous solution (80° C.) of HCl: 50 cc in 1500 cc of a distilledwater for 1 minute.

(D) Step

The oxide on the surface of the steel sheet is removed by immersing inan aqueous solution (80° C.) of HCl: 50 cc in 1500 cc of a distilledwater for 0.5 minute and then chemical polishing is carried out in amixed solution of 3%HF and 97%H₂O₂.

(E) Step

After the treatment of the step (D), the same method as in the step (A)is carried out or the steel sheet is immersed in an aqueous solution(80° C.) of SiCl₄: 30 cc in 1500 cc of a distilled water for 20 seconds.

Thereafter, the silicon steel sheets treated at the above (A)˜(E) stepsare treated in a mixed gas of H₂(50%)+N₂(50%) at 950° C. for 10 minutes,immersed in a treating solution of 80° C. formed by adding SiCl₄solution: 25 cc, FeCl₃: 15 g, AlPO₄: 10 g and H₃PO₃: 10 g together to adiluted solution obtained by diluting a coating solution for tensioninsulating film on the surface of the silicon steel sheet consistingessentially of phosphate and colloidal silica: 250 cc in 1500 cc of adistilled water for 20 minutes, washed with water and dried.

Then, the steel sheet is subjected to a heat treatment in a mixed gas ofN₂(93%)+H₂(7%) at 900° C. for 10 minutes.

Moreover, as (A′) step, after the treatment of the (A) step, anextremely thin base film is formed on the surface of the steel sheet bymerely exposing in N atmosphere for 20 seconds without conducting theheat treatment in the mixed atmosphere of H₂(50%)+N₂(50%) for a shorttime and then conducting the same treatment as mentioned above in amixed gas of N₂(93%)+H₂(7%).

Thereafter, a coating solution of tension insulating film consistingessentially of phosphate and colloidal silica is applied onto thesurface of the steel sheet and dried and baked in N₂ gas at 800° C. toform a tension insulating film having a thickness of 2.0 μm.

The core loss property W_(17/50) (W/kg) and adhesion property of thethus obtained products are measured to obtain results as shown in Table4.

TABLE 4 Magnetic Adhesion property properties (diameter causing B₈W_(17/50) no peeling by Step Treating method (T) (W/kg) 180° bending)(A) immersion in aqueous solution 1.91 0.63 20 mmφ Invention containingSiCl₄ (30 cc) for Example 1 minute (A′) after step (A), exposuretreatment 1.91 0.61 20 mmφ Invention in N-containing non-oxidizingExample atmosphere (B) immersion in aqueous solution 1.91 0.65 25 mmφInvention containing SiCl₄ (20 cc) and Example HC1 (20 cc) for 1 minute(C) immersion in aqueous solution 1.90 0.78 X Comparative containing HCl(50 cc) for (peeling) Example 1 minute (D) immersion in aqueous solutionComparative containing HCl (50 cc) for 1.91 0.70 X Example 0.5 minuteand chemical polishing (peeling) in a mixed solution of 3% HF and 97%H₂O₂ (E) immersion in aqueous solution 1.91 0.56 20 mmφ Inventioncontaining HCl (50 cc) for Example 0.5 minute and chemical polishing ina mixed solution of 3% HF and 97% H₂O₂ and further immersion in aqueoussolution containing SiCl₄ (30 cc) for 20 seconds

As seen from Table 4, in the silicon steel sheets treated at the (A),(A′), (B) and (E) steps according to the invention, it is noticed thatultra-low core loss of 0.56˜0.65 W/kg is obtained as the core lossW_(17/50) (W/kg) and the adhesion property is good.

That is, it is noticed that it is possible to produce grain orientedsilicon steel sheets having ultra-low core loss and an excellentadhesion property by immersing a grain oriented silicon steel sheethaving no forsterite film in an aqueous solution containing SiCl₄ andthen subjecting to a pickling treatment. Moreover, it is noticed that aparticularly better result is obtained by conducting the picklingtreatment and the chemical polishing treatment as in the (E) step, butultra-low core loss of 0.63 W/kg and 0.61 W/kg as W_(17/50) (W/kg) isobtained even at the (A) and (A′) steps not conducting the chemicalpolishing.

Heretofore, there is adopted a method of reducing hysteresis loss of thesilicon steel sheet by smoothening the surface of the silicon steelsheet through chemical polishing, electrolytic polishing or the like.

However, the chemical polishing, electrolytic polishing methods have agreat problem that the product yield is poor and the polishing costlargely increases.

In the invention, it is noticed that the grain oriented silicon steelsheet having a ultra-low core loss and an excellent adhesion property isobtained very cheaply only by subjecting a surface of a grain orientedsilicon steel sheet having no forsterite base film to immersion-picklingtreatment in an aqueous solution containing SiCl₄.

In FIG. 6 is shown a result of N concentration in a surface portion of asteel sheet as measured by SIMS (Secondary Ion Mass Spectroscopy) whenthe steel sheet after the final annealing is immersed in SiCl₄ solution(80° C.) and exposed in N atmosphere according to the (A′) step ascompared with the case of chemical polishing in a mixed solution of 3%HFand 97%H₂O₂ according to the (D) step.

As shown in this figure, it is noticed that when the steel sheet isimmersed in the SiCl₄ solution and then exposed in the N atmosphere, aconsiderably high N-enriched layer is formed on the surface of the steelsheet as compared with the chemically polished material.

As being described based on Experiments 1˜5, according to the invention,the interface layer such as nitride-oxide layer of one or more selectedfrom Fe, Si, Al and B or extremely thin base film formed by finelydispersing nitride-oxide of one or more selected from Fe, Si, Al and Binto the same film components as in the tension insulating film isformed at the interface between the matrix surface of the silicon steelsheet and the tension insulating film, or further prior to the formationof such an interface layer, the matrix surface is dissolved by immersingin an aqueous solution of a chloride mainly composed of SiCl₄ or thesmoothening treatment or pickling treatment is carried out by using theaqueous solution containing SiCl₄, whereby the adhesion property of thefilm to the matrix surface can considerably be improved and henceultra-low core loss grain oriented silicon steel sheets having aconsiderably excellent core loss property as compared with theconventional material and an excellent magnetostriction property can beobtained very cheaply and in a high productivity.

As silicon-containing steel of a starting material according to theinvention, any of conventionally known compositions are adaptable, andtypical composition is mentioned as follows.

C: 0.01˜0.08 wt %

When C amount is less than 0.01 wt %, the control of hot rolled textureis insufficient and a largely grown grains are formed to degrade themagnetic properties, while when it exceeds 0.08 wt %, a long time isuneconomically taken at decarburization step, so that it is favorable tobe about 0.01˜0.08 wt %.

Si: 2.0˜4.0 wt %

When Si amount is less than 2.0 wt %, sufficient electric resistance isnot obtained and hence eddy current loss increases to bring aboutdegradation of core loss, while when it exceeds 4.0 wt %, brittle crackis easily caused in the cold rolling, so that it is favorable to bewithin a range of about 2.0˜4.0 wt %.

Mn: 0.01˜0.2 wt %

Mn is an important element determining MnS or MnSe as a dispersionprecipitate phase depending the secondary recrystallization of the grainoriented silicon steel sheet. When Mn amount is less than 0.01 wt %, anabsolute amount of MnS or the like required for causing the secondaryrecrystallization is lack and incomplete secondary recrystallization iscaused and at the same time surface defect called as blister increases.While, when it exceeds 0.2 wt %, even if dissociation and solid solutionof MnS and the like are carried out in the slab heating or the like, thedispersion precipitate phase precipitated in the hot rolling is apt tobe coarsened and optimum size distribution desired as an inhibitor isdamaged to degrade the magnetic properties. Therefore, Mn is favorableto be about 0.01˜0.2 wt %.

S: 0.008˜0.1 wt %, Se: 0.003˜0.1 wt %

Each of S and Se is favorable to be not more than 0.1 wt %, andpreferably S is within a range of 0.008˜0.1 wt % and Se is within arange of 0.003˜0.1 wt %. When they exceed 0.1 wt %, hot workability andcold workability are degraded, while when each of them is less thanlower limit, a considerable effect is not caused in the function ofcontrolling primary grain growth as MnS, MnSe.

Besides, even when Al, Sb, Cu, Sn, B and the like conventionally knownas an inhibitor are added together, the effect of the invention is notobstructed.

The production steps of the ultra-low core loss grain oriented siliconsteel sheet according to the invention will be described below.

In order to melt the starting material, LD converter, electric furnace,open-hearth furnace and other known steel-making furnaces can be usedbut also vacuum melting or RH degassing treatment may be used together.

According to the invention, S, Se or other primary grain growthcontrolling agent included in the starting material can be added tomolten steel in a slight amount by anyone of the conventionally knownmethods. For example, it can be added in molten steel in LD converter,or after the completion of RH degassing or in the ingot making.

And also, in the production of a slab, it is advantageous to adopt acontinuous casting method in view of economical and technical meritssuch as cost reduction, uniformity of component or quality inlongitudinal direction of the slab, but the use of conventional ingotmaking slab is not obstructed.

The continuously cast slab is heated to a temperature of not lower than1300° C. for dissociation and solid solution of inhibitor in the slab.Thereafter, the slab is subjected to rough hot rolling and subsequentlyhot finish rolling to obtain a hot rolled sheet having usually athickness of about 1.3˜3.3 mm.

Then, the hot rolled sheet is subjected to cold rolling twice through anintermediate annealing within a temperature range of 850˜1100° C., ifnecessary to a final sheet thickness. In this case, it is required totake a care on final cold rolling ratio (usually 55˜90%) for obtaining aproduct having properties such as high magnetic flux density and lowcore loss.

From a viewpoint that eddy current loss of the silicon steel sheet isdecreased as much as possible, the upper limit of the product thicknessis 0.5 mm, while the lower limit of the sheet thickness is 0.05 mm foravoiding deterioration of hysteresis loss.

Particularly, when the linear grooves are formed on the surface of thesteel sheet, it is advantageous to conduct this formation to the steelsheet having a product thickness after the final cold rolling.

That is, linear concave regions having width: 50˜500 μm and depth:0.1˜50 μm are formed on the surface of the final cold rolled sheet orthe steel sheet before and after secondary recrystallization at aninterval of 2˜10 mm in a direction crossing the rolling direction.

The reason why the interval between the linear concave regions islimited to 2˜10 mm is due to the fact that when it is less than 2 mm,the irregularities of the steel sheet become considerably conspicuousand the magnetic flux density uneconomically lowers, while when itexceeds 10 mm, the effect of finely dividing magnetic domain becomessmaller.

When the width of the concave region is less than 50 μm, it is difficultto utilize the anti-magnetic field effect, while when it exceeds 500 μm,the magnetic flux density uneconomically lowers, so that the width ofthe concave region is limited to a range of 50˜500 μm.

When the depth of the concave region is less than 0.1 μm, theanti-magnetic field effect can not effectively be utilized, while whenit exceeds 50 μm, the magnetic flux density uneconomically lowers, sothat the depth of the concave region is limited to a range of 0.1˜50 μm.

Moreover, the forming direction of the linear concave region is optimumto be a direction perpendicular to the rolling direction or thewidthwise direction of the sheet. However, substantially the same effectcan be obtained when it is within ±30° to the widthwise direction.

As the method of forming the linear concave regions, a method wherein anetching resist is applied onto the surface of the final cold rolledsheet by printing and baked and the etching treatment is conducted andthereafter the resist is removed is advantageous as compared with theconventional method using a knife blade, a laser or the like in a pointthat it can stably be carried out in industry and a point that the coreloss can be reduced more effectively by tensile tension.

A typical example of the technique for the formation of linear groovesthrough the above etching will be described concretely below.

An etching resist ink mainly composed of alkyd resin is coated onto thesurface of the final cold rolled sheet by gravure offset printing so asto leave non-coated portions of width: 200 μm at an interval: 4 mm in adirection substantially perpendicular to the rolling direction, andbaked at 200° C. for about 20 seconds. In this case, the resistthickness is about 2 μm. The steel sheet coated with the etching resistis subjected to an electrolytic etching or a chemical etching to formlinear grooves having width: 200 μm and depth: 20 μm, and then it isimmersed in an organic solvent to remove the resist. In this case, it isfavorable that the electrolytic etching conditions are current density:10 A/dm² and treating time: about 20 seconds in NaCl electrolyte, andthe chemical etching condition is immersion time: about 10 seconds inHNO₃ solution.

Then, the steel sheet is subjected to decarburization annealing. Thisannealing is to render the cold rolled structure into a primaryrecrystallization structure and at the same time remove harmful C whensecondary recrystallized grains of {110} <001> orientation are grown ata final annealing (which may be called as a final annealing), and iscarried out, for example, in a wet hydrogen at 750˜880° C.

The final annealing is to sufficiently develop the secondaryrecrystallized grains of {110} <001> orientation, and is usually carriedout by raising temperature above 1000° C. immediately in box annealingand holding this temperature. Usually, the final annealing is carriedout by applying an annealing separator such as magnesia or the like,wherein a base film called as forsterite is simultaneously formed on thesurface.

In the invention, however, even when the forsterite base film is formed,such a base film is removed at subsequent step, so that it isadvantageous to use an annealing separator not forming the forsteritebase film. That is, it is advantageous to use an annealing separatorwherein the content of MgO forming the forsterite base film is decreased(not more than 50%) and the content of CaO, Al₂O₃, CaSiO₃, SiO₂, PbCl₃or the like not forming such a film is increased (not less than 50%).

In the invention, it is advantageous to conduct a temperature-holdingannealing at a low temperature of from 820° C. to 900° C. for developingthe secondary recrystallized texture highly aligned in {110} <001>orientation, but a slow-heating annealing at a temperature rising rateof, for example, 0.5˜15° C./h may be conducted.

After such a purification annealing, the forsterite base film or oxidefilm on the surface of the surface of the steel sheet is removed by achemical method such as conventionally known pickling or the like, amechanical method such as cutting, polishing or the like, or acombination of these methods, whereby the surface of the steel sheet issmoothened.

That is, after the various films are removed from the surface of thesteel sheet, the steel sheet surface is smoothened to a center lineaverage roughness Ra of about not more than 0.4 μm by the conventionalmethod being chemical polishing such as chemical polishing, electrolyticpolishing or the like, mechanical polishing such as buffing or the like,or a combination thereof.

In the invention, it is not necessarily required to smoothen the surfaceof the silicon steel sheet. In this case, therefore, there is a meritthat the sufficient effect of reducing the core loss can be developedonly by the pickling treatment without the smoothening treatmentaccompanied with the cost-up. However, it is unchanged that thesmoothening treatment is advantageous.

At this stage, concaved grooves can be formed on the surface of thesteel sheet. The formation of the groove may be conducted by the samemethod as in the case of forming on the surface of the final cold rolledsheet or the steel sheet before or after the secondaryrecrystallization.

According to the invention, the above treated steel sheet is subjectedto the formation of nitride-oxide layer of one or more selected from Fe,Si, Al and B as an interface layer prior to the formation of a tensioninsulating film on a matrix surface of the silicon steel sheet.

In this case, an extremely thin Si-containing nitride-oxide layer isoptimum as the above nitride-oxide layer.

A preferable method of forming the extremely thin Si-containingnitride-oxide layer is a method wherein a solution containing Sicompound, e.g. a diluted aqueous solution containing SiCl₄ is appliedonto the surface of the steel sheet to adhere a slight amount of Si atan active state and a heat treatment is carried out in a non-oxidizingatmosphere for a short time.

According to this method, a desired film can be obtained very cheaplyand for a short time because a long-time treatment at a high cost as inthe treatment under vacuum in a high plasma atmosphere is not required.

As the atmosphere in the heat treatment for short time for forming theabove nitride-oxide layer, a N-containing non-oxidizing atmosphere ispreferable for promoting nitriding, and an atmosphere of a (N₂+H₂) mixedgas is particularly favorable.

And also, it is favorable that the treating temperature is about80˜1200° C. (preferably about 500˜1100° C.) and the treating time isabout 1˜100 minutes (preferably about 3˜30 minutes).

Another preferable method is a method wherein the steel sheet isimmersed in a solution containing Si compound to adhere a slight amountof Si at an active state onto the surface and exposed in a N-containingnon-oxidizing atmosphere.

Since such an immersion treatment is usually carried out at a bathtemperature of about 90° C., even when the exposure in the N-containingnon-oxidizing atmosphere is conducted after the immersion, the extremelythin nitride-oxide layer containing Si is formed on the surface of thesteel sheet.

The composition of the oxide in the nitride-oxide layer containing Si ismainly composed of FeSiO₃ and Fe₂SiO₄ as shown in FIG. 4. These oxidesare very dense different from the conventional sub-scale of SiO₂ andthese dense oxides are produced together with fine nitride, so that itis considered to considerably improve the adhesion property as comparedwith the conventional one.

In the invention, the above heat treatment for short time and exposuretreatment in the N-containing non-oxidizing atmosphere are not alwaysrequired.

Because, even when the heat treatment for short time is not carried out,the Si-containing nitride-oxide layer is preferentially formed on thesurface of the steel sheet by a heat treatment in the subsequentformation of an insulating film.

The Si-containing nitride-oxide layer is favorable to be about 0.001˜0.1μm. When the film thickness is less than 0.001 μm, the sufficientadhesion property and hence the effect of reducing the core loss are notobtained, while when it exceeds 0.1 μm, the Si amount becomes too largeand it is difficult to satisfactorily form the nitride-oxide layer of Siand hence the improvement of not only the magnetic properties but alsothe adhesion property to the film are not expected.

In order to obtain the above film thickness, the amount of the solutioncontaining Si compound applied to the steel sheet surface is dependentupon the concentration thereof, but is favorable to be about 0.001˜2.0g/m². It is more preferably within a range of 0.01˜1.0 g/m².

As the application method, use may be made of any conventionally knownmethods such as immersion method of immersing the steel sheet itself ina solution, electrolytic treating method and the like in addition toapplication by means of usual roll coater or the like. The treatingtemperature may be room temperature, but it is preferable to treat in awarm solution of about 50˜100° C. for more effectively conducting theadhesion.

As the Si compound, all of compounds capable of adhering Si at an activestate are advantageously adaptable, and the preferable compound isSiCi₄.

In the invention, it is required to adhere Si onto the surface of thesteel sheet at an active state, so that the previously deactivated oxideor nitride is excluded as the Si compound is used.

In the other embodiment, after Si is thinly formed by PVD or CVD (Sicontent: about 0.001˜0.2 g/m²), it is sufficient to conduct a heattreatment in the non-oxidizing atmosphere for a short time.

Although the rise of the cost is unavoidable, the film thickness can bemade extremely thin, so that the cost can be decreased by the thinnedthickness as compared with the conventional one.

As the PVD, vapor deposition, ion plating and the like areadvantageously adaptable in addition to the above magnetron sputteringmethod. In this case, the Si film may be crystalline or amorphous. Inother words, it is sufficient to be at an active state capable ofbonding to N or O.

Thereafter, the coating solution for tension insulating film consistingessentially of a phosphate and colloidal silica is coated onto thesurface of the silicon steel sheet according to the usual manner andbaked at 500˜1000° C. to form a tension insulating film (film thickness:0.5˜5 μm).

As the coating solution for tension insulating film consistingessentially of phosphate and colloidal silica, there are advantageouslyadapted a coating solution containing colloidal silica: 4˜16 wt %,aluminum phosphate: 3˜24 wt % and chromic anhydride and/or chromate:0.2˜4.5 wt % as disclosed in JP-B-53-28375, and a coating solutioncontaining colloidal silica: 7˜24 wt %, magnesium phosphate: 5˜30 wt %(provided that a molar ratio of magnesium phosphate to colloidal silicais 20/80˜30/70), and if necessary, chromic anhydride, chromate and/ordichromate: 0.01˜5 wt % as disclosed in JP-B-56-52117.

The case that the extremely thin base film is formed as an interfacelayer by finely dispersing nitride-oxide of one or more selected fromFe, Si, Al and B into the same film components as the tension insulatingfilm prior to the formation of the tension insulating film on the matrixsurface of the silicon steel sheet will be described below.

In the formation of such an extremely thin base film, a coating solutionfor tension insulating film consisting essentially of phosphate andcolloidal silica is first diluted with water and a slight amount of aninorganic compound containing one or more selected from Fe, Si, Al and Bis added to the diluted solution to form a treating solution.

In the application onto the steel sheet surface, the above treatingsolution is directly applied onto the surface of the silicon steelsheet, but the treating solution may be applied after an aqueoussolution added with the inorganic compound of Fe, Si, Al, B and the likeis previously applied onto the steel sheet surface.

In this case, the coating solutions disclosed in JP-B-53-28375 andJP-B-56-52117 as mentioned above are advantageously adapted as thecoating solution for tension insulating film consisting essentially ofphosphate and colloidal silica.

And also, the coating solution is favorable to be diluted to a dilutingdegree of about 0.1˜60%, preferably 1˜20% (for example, amount ofdiluting about 10˜1000 cc of the coating solution into 1500 cc ofwater).

In the invention, it is necessary to change the inorganic compound ofFe, Si, Al, B and the like included in the underground treating solutioninto nitride-oxide for forming the base film strongly adhered to thematrix, but when the concentration of the underground treating solutionis too thick, it is difficult to well change the inorganic compound intonitride-oxide in the treating atmosphere (preferably mixed gasatmosphere of N₂(50%)+H₂(50%)) and it is effective to dilute with aproper amount of water for effectively promoting nitriding-oxidation.

Further, the addition amount of the inorganic compound containing one ormore selected from Fe, Si, Al and B in the diluted solution is favorableto be about 5˜500 g per liter (about 0.001˜0.5 mol/l) as the amount ofthe inorganic compound.

Because, when the amount of the inorganic compound is too small, theeffect can not be developed, while when it is too large, the economicalmerit is not obtained and the film properties are rather degraded.

Among various inorganic compounds, it is particularly advantageous touse FeCl₃, Fe(NO₃)₃ and the like as Fe-containing inorganic compound,SiCl₄, Na₂SiO₃, SiO₂ and the like as Si-containing inorganic compound,AlCl₃, Al(NO₃)₃, AlPO₄ and the like as Al-containing inorganic compound,and H₃BO₃, Na₂B₄O₇ and the like as B-containing inorganic compound.

After a slight amount of the inorganic compound of Fe, Si, Al, B and thelike is adhered to the matrix surface by applying the treating solutionobtained by adding a slight amount of the inorganic compound of Fe, Si,Al, B and the like to the diluted solution of the coating solution fortension insulating film onto the steel sheet surface and drying it asmentioned above, it is subjected to a heat treatment in, preferably, anon-oxidizing atmosphere for a short time, whereby an extremely thinbase film finely dispersing nitride-oxide of Fe, Si, Al, B and the likeinto the tension insulating film components is formed on the surface ofthe steel sheet.

Moreover, the invention does not necessarily require the heat treatmentfor short time as mentioned above. Because, even when the heat treatmentfor short time is not carried out, the extremely thin base film finelydispersed with nitride-oxide of Fe, Si, Al, B and the like as mentionedabove is preferentially formed on the steel sheet surface by subsequentheat treatment for the formation of the tension insulating film.

As the application method, use may be made of any conventionally knownmethods such as immersion method of immersing the steel sheet itself ina solution, method of directly spraying or jetting the treating solutionto the steel sheet surface, electrolytic treating method and the like inaddition to application by means of usual roll coater or the like. Thetreating temperature may be room temperature, but it is preferable totreat in a warm solution of about 50˜100° C. for more effectivelyconducting the adhesion. And also, in case of utilizing the immersionmethod, the immersing time is desirable to be about 1˜100 seconds.

In order to form fine nitride-oxide of Fe, Si, Al, B and the like on thesurface of the steel sheet after the washing with water and drying, itis more preferably subjected to a heat treatment in a non-oxidizingatmosphere for a short time.

As the treating atmosphere, N-containing non-oxidizing atmosphere isfavorable for promoting nitriding, and particularly atmosphere of(N₂+H₂) mixed gas and (NH₃+H₂) mixed atmosphere containing ammonia arepreferable.

And also, it is favorable that the treating temperature is about200˜1200° C. (preferably about 500˜1000° C.) and the treating time isabout 1˜100 minutes (preferably about 3˜30 minutes).

Thus, the extremely thin base film strongly adhered to the surface ofthe steel sheet can be formed under the presence of nitride-oxide of Fe,Si, Al, B and the like finely dispersed in the film.

Moreover, the application amount of the underground treating solution isfavorable to be about 0.001˜0.5 g/m². After the application of such anamount, the heat treatment is carried out, whereby there can finally beobtained the extremely thin base film having a preferable thickness ofabout 0.001˜3.0 μm.

Thereafter, the coating solution for tension insulating film consistingessentially of colloidal silica and phosphate is coated onto the surfaceof the above extremely thin base film and baked at a temperature of500˜1000° C. to from a tension insulating film (thickness: 0.5˜5 μm).

In this case, the extremely thin base film is the same material as thetension insulating film formed thereon, so that the adhesion propertytherebetween is very high and hence the tension insulating film having aconsiderably excellent adhesion property as compared with theconventional one can be formed on the surface of the steel sheet. Thus,the grain oriented silicon steel sheet having a very low core loss canbe obtained in a high productivity and a low cost.

In occasion, it is possible to use an insulating film consistingessentially of a phosphate and chromic acid and containing no colloidalsilica in the film as the insulating film.

And also, in order to more develop an inclination function to thesilicon steel sheet, it is advantageous that usual insulating film isfirst formed on the silicon steel sheet and then a tension insulatingfilm is formed thereon.

A pretreatment prior to the formation of the extremely thin base filmthat the silicon steel sheet is immersed in an aqueous solution of SiCl₄of a chloride mainly composed of SiCl₄ to dissolve a surface of a matrixto a certain extent will be described below.

The reason why the above pretreatment is carried out is due to the factthat the activity of the matrix surface and hence the adhesion propertyare enhanced by dissolving Fe component on the surface of the matrix toa certain extent as previously mentioned.

In this case, the preferable amount of the matrix surface to bedissolved is within a range of about 0.01˜3.0 μm as a decreased amountof sheet thickness (about 0.0005˜0.15 g as a weight reduction amount) asshown in FIG. 5.

Moreover, the sheet thickness decreased amount is determined by only thepretreatment when the chloride such as SiCl₄ or the like is not used asthe inorganic compound added to the treating solution in the subsequentformation of the base film. However, when the chloride is used as theinorganic compound, the matrix is somewhat dissolved by the applicationof the treating solution for the formation of the base film. In thelatter case, the sheet thickness decreased amount is evaluated as avalue after the treatment for the formation of the base film.

As the chloride other than SiCl₄, MgCl₂, CaCl₂, SrCl₂, BaCl₂ and thelike are advantageously adaptable, but TiCl₃, ZrCl₄, NbCl₅, TaCl₅,CrCl₃, CoCl₃, NiCl₂, CuCl₂, ZnCl₂, TlCl₃ or the like may be used in avery slight amount.

Further, the aqueous solution of the chloride may be sprayed or jettedto the surface of the steel sheet instead of the immersion treatment ofthe silicon steel sheet in the aqueous solution of the chloride.

After the above pretreatment, it is advantageous that the surface of thesilicon steel sheet is subjected to so-called exposure treatmentexposing in N-containing non-oxidizing atmosphere.

Because, N enriched layer is formed on the surface of the steel sheet bysuch an exposure treatment (it is considered to form nitride-oxide layerof Si), which advantageously contributes to the improvement of theadhesion property to the film.

And also, an annealing treatment in a non-oxidizing atmosphere above500° C. may be carried out instead of the above exposure treatment.

Then, an extremely thin film finely dispersing nitride-oxide of one ormore selected from Fe, Si, Al and B into the same film components as thetension insulating film consisting essentially of phosphate andcolloidal silica is formed as a base film by the method as mentionedabove.

As a base of the above extremely thin film, the tension insulating filmconsisting essentially of phosphate and colloidal silica is notnecessarily required, but the usual insulating film consistingessentially of phosphate and chromic acid may be used.

There will be described a case that a pickling treatment or asmoothening treatment is carried out in an aqueous solution containingSiCl₄ in case of the pickling treatment or further the smootheningtreatment as a surface treatment of the silicon steel sheet after thefinal annealing.

In this case, the SiCl₄ concentration in the aqueous solution used isdesirable to be about 0.001˜5.0 mol/l. When the concentration is toothick, economical merit is not obtained, while when it is too thin, thetreating effect is lessened.

In case of using SiCl₄, the incorporation of HCl, H₃PO₄, H₂SO₄, HF orthe like as shown in the (B) step in Table 1, or the use of the otherchloride compound, for example, addition of a small amount of FeCl₃,AlCl₃ or the like is not obstructed.

Further, the aqueous solution containing SiCl₄ is effective as anelectrolyte, so that the surface of the silicon steel sheet may besubjected to a weak electrolytic treatment. And also, it is possible todirectly spray or jet the aqueous solution onto the steel sheet insteadof the immersion or electrolytic treatment.

After such a pretreatment, it is advantageous that the surface of thesilicon steel sheet is subjected to so-called exposure treatmentexposing in N-containing non-oxidizing atmosphere.

Because, N enriched layer is formed on the surface of the steel sheet bysuch an exposure treatment (it is considered to form nitride-oxide layerof Si), which advantageously contributes to the improvement of theadhesion property to the film.

And also, an annealing treatment in a non-oxidizing atmosphere above500° C. may be carried out instead of the above exposure treatment.

Then, an extremely thin film finely dispersing nitride-oxide of one ormore selected from Fe, Si, Al and B into the same film components as thetension insulating film consisting essentially of phosphate andcolloidal silica is formed as a base film by the method as mentionedabove.

As a base of the above extremely thin film, the tension insulating filmconsisting essentially of phosphate and colloidal silica is notnecessarily required, but the usual insulating film consistingessentially of phosphate and chromic acid may be used.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing magnetostriction of silicon steel sheet as acomparison between invention example and conventional example;

FIG. 2 is a diagrammatic view showing a section near to surface as acomparison between the existing grain oriented silicon steel sheet (FIG.2a) and a grain oriented silicon steel sheet provided with a tensioninsulating film formed on an extremely thin Si-containing nitride-oxideaccording to the invention (FIG. 2b);

FIG. 3 is a diagrammatic view showing a section near to surface as acomparison among the conventional grain oriented silicon steel sheetobtained by merely forming a tension insulating film consistingessentially of phosphate and colloidal silica on a surface of the grainoriented silicon steel sheet after final annealing (FIG. 3a), theconventional grain oriented silicon steel sheet obtained by forming anextremely thin ceramic film of TiN, CrN or the like on a smoothenedsurface of the grain oriented silicon steel sheet and further forming atension insulating film thereon (FIG. 3b), and a grain oriented siliconsteel sheet according to the invention obtained by forming an extremelythin base film finely dispersed with a slight amount of nitride-oxide ofFe, Si, Al, B and the like at an interface between the grain orientedsilicon steel sheet and the tension insulating film (FIG. 3c);

FIG. 4 is a graph showing an oxide composition in nitride-oxide of Sidispersed in the extremely thin base film;

FIG. 5 is a graph showing a relation between decreased amount of sheetthickness prior to the application of a coating solution for tensioninsulating film and core loss W_(17/50) (W/kg) of a product sheet; and

FIG. 6 is a graph showing a comparison of surface N concentrationbetween chemical polished material and SiCl material.

BEST MODE FOR CARRYING OUT THE INVENTION EXAMPLE 1

A continuously cast slab of silicon steel having a composition of C:0.078 wt %, Si: 3.45 wt %, Mn: 0.076 wt %, Se: 0.021 wt %, Sb: 0.025 wt%, Al: 0.024 wt %, N: 0.0073 wt % and Mo: 0.012 wt % and the remainderbeing substantially Fe is heated at 1350° C. for 4 hours and hot rolledto obtain a hot rolled sheet of thickness: 2.2 mm. Then, the hot rolledsheet is subjected to normalization annealing at 1000° C. and coldrolled twice through an intermediate annealing at 1050° C. to obtain afinal cold rolled sheet of thickness: 0.23 mm.

After the decarburization and primary recrystallization annealing in wetH₂ of 850° C., a slurry of an annealing separator having a compositionof MgO(20%), Al₂O₃(70%) and CaSiO₃(10%) is applied to the surface of thesteel sheet and annealed at 850° C. for 15 hours and temperature israised from 850° C. to 1180° C. at a rate of 12° C./h to developsecondary recrystallized grains strongly aligned in Goss orientation andsubjected to purification annealing in dry H₂ of 1220° C.

The thus obtained silicon steel sheet is subjected to either {circlearound (1)} a smoothening treatment through chemical polishing or{circle around (2)} a pickling treatment with 10% HCl after the removalof oxide film from the surface.

Then, the silicon steel sheet is immersed in an aqueous solution (80C.)of SiCl₄ (0.3 mol/l) for 10 minutes and treated in a mixed gas ofN₂(50%)+H₂(50%) at 950° C. for 10 minutes. Thereafter, a tensioninsulating film (thickness of about 2 μm) consisting essentially ofcolloidal silica and phosphate is formed on the surface of the steelsheet and baked at 800° C.

The magnetic properties, adhesion property and compression stressproperty of magnetostriction in the thus obtained product are asfollows.

{circle around (1)} In case of the smoothening treatment

Magnetic properties B₈: 1.95 T W_(17/50): 0.68 W/kg Adhesion propertygood without peeling by 180° bending on a round rod of diameter: 20 mmMagnetostriction magnetic strain λ_(pp) = 0.8 × 10⁻⁶ at compressionstress σ = 0.4 kg/mm², magnetic strain λ_(pp) = 1.1 × 10⁻⁶ atcompression stress σ = 0.6 kg/mm²

{circle around (2)} In case of the pickling treatment

Magnetic properties B₈: 1.94 T W_(17/50): 0.70 W/kg Adhesion propertygood without peeling by 180° bending on a round rod of diameter: 20 mmMagnetostriction magnetic strain λ_(pp) = 0.7 × 10^(−6 at) compressionstress σ = 0.4 kg/mm², magnetic strain λ_(pp) = 1.2 × 10⁻⁶ atcompression stress σ = 0.6 kg/mm²

For the comparison, after the decarburization and primaryrecrystallization annealing in wet H₂ of 850° C., a slurry of anannealing separator mainly composed of MgO is applied to the surface ofthe steel sheet and annealed at 850° C. for 15 hours and temperature israised from 850° C. to 1180° C. at a rate of 10° C./h to developsecondary recrystallized grains strongly aligned in Goss orientation andsubjected to purification annealing in dry H₂ of 1200° C. Thereafter, atension insulating film (thickness of about 2 μm) consisting essentiallyof colloidal silica and phosphate is formed on a forsterite base filmand baked at 800° C. The magnetic properties, adhesion property andcompression stress property of magnetostriction in the thus obtainedgrain oriented silicon steel sheet are measured to obtain results asfollows.

Magnetic properties B₈: 1.95 T W_(17/50): 0.80 W/kg Adhesion property nopeeling by 180° bending on a round rod of diameter: 20 mmMagnetostriction magnetic strain λ_(pp) = 1.6 × 10⁻⁶ at compressionstress σ = 0.4 kg/mm², magnetic strain λ_(pp) = 5.3 × 10⁻⁶ atcompression stress σ = 0.6 kg/mm²

EXAMPLE 2

A continuously cast slab of silicon steel having a composition of C:0.066 wt %, Si: 3.49 wt %, Mn: 0.072 wt %, Se: 0.020 wt %, Sb: 0.025 wt%, Al: 0.022 wt %, N: 0.0068 wt % and Mo: 0.012 wt % and the remainderbeing substantially Fe is heated at 1340° C. for 5 hours and hot rolledto obtain a hot rolled sheet of thickness: 2.0 mm. The hot rolled sheetis subjected to normalization annealing at 950° C. and cold rolled twicethrough an intermediate annealing at 1050° C. to obtain a final coldrolled sheet of thickness: 0.23 mm.

Then, an etching resist ink consisting essentially of an alkyd resin isapplied onto the surface of the final cold rolled sheet by gravureoffset printing so as to leave linear non-coated portions of width: 200μm at an interval: 4 mm in a direction substantially perpendicular to arolling direction, and baked at 200° C. for about 2 seconds. In thiscase, a resist thickness is 2 μm. The steel sheet coated with theetching resist is subjected to an electrolytic etching to form lineargrooves of width: 200 μm and depth: 20 μm and then immersed in anorganic solvent to remove the resist. In this case, the electrolyticetching is carried out in NaCl electrolyte under conditions of currentdensity: 10 A/dm² and treating time: 20 seconds.

After the decarburization and primary recrystallization annealing in wetH₂ of 840° C., a slurry of an annealing separator having a compositionof MgO(25%), Al₂O₃(70%) and CaSiO₃(5%) is applied to the surface of thesteel sheet and annealed at 850° C. for 15 hours and temperature israised from 850° C. to 1150° C. at a rate of 10° C./h to developsecondary recrystallized grains strongly aligned in Goss orientation andsubjected to purification annealing in dry H₂ of 1200° C.

The surface of thus obtained grain oriented silicon steel sheet issmoothened through chemical polishing after the removal of oxide filmfrom the surface of the silicon steel sheet.

Then, the silicon steel sheet is immersed in an aqueous solution (80°C.) of SiCi₄ (0.3 mol/l) for 10 seconds and treated in a mixed gas ofN₂(50%)+H₂(50%) at 900C. for 10 minutes. Thereafter, a tensioninsulating film (thickness of about 2 μm) consisting essentially ofcolloidal silica and phosphate is formed on the surface of the steelsheet and baked at 800° C.

The magnetic properties and adhesion property in the thus obtainedproduct are as follows.

Magnetic properties B₈: 1.91 T W_(17/50): 0.59 W/kg Adhesion propertygood without peeling by 180° bending on a round rod of diameter: 20 mm

And also, an extremely thin Si-containing nitride-oxide layer is formedon the surface of as-pickled steel sheet without chemical polishing andthen a tension insulating film of a phosphate is formed thereon. Themagnetic properties and adhesion property in the thus obtained productare as follows.

Magnetic properties B₈: 1.92 T W_(17/50): 0.64 W/kg Adhesion propertygood without peeling by 180° bending on a round rod of diameter: 20 mm

EXAMPLE 3

A continuously cast slab of silicon steel having a composition of C:0.044 wt %, Si: 3.39 wt %, Mn: 0.073 wt %, Se: 0.020 wt %, Sb: 0.025 wt% and Mo: 0.012 wt % and the remainder being substantially Fe is heatedat 1340° C. for 3 hours and hot rolled to obtain a hot rolled sheet ofthickness: 2.4 mm. The hot rolled sheet is subjected to normalizationannealing at 900° C. and cold rolled twice through an intermediateannealing at 950° C. to obtain a final cold rolled sheet of thickness:0.23 mm.

Then, an etching resist ink consisting essentially of an alkyd resin isapplied onto the surface of the final cold rolled sheet by gravureoffset printing so as to leave linear non-coated portions of width: 200μm at an interval: 4 mm in a direction substantially perpendicular to arolling direction, and baked at 200° C. for about 20 seconds. In thiscase, a resist thickness is 2 μm. The steel sheet coated with theetching resist is subjected to an electrolytic etching to form lineargrooves of width: 200 μm and depth: 20 μm and then immersed in anorganic solvent to remove the resist. In this case, the electrolyticetching is carried out in NaCl electrolyte under conditions of currentdensity: 10 A/dm² and treating time: 20 seconds.

After the decarburization and primary recrystallization annealing in wetH₂ of 840° C., a slurry of an annealing separator having a compositionof MgO(25%), Al₂O₃(70%) and CaSiO₃(5%) is applied to the surface of thesteel sheet and subjected to a temperature-holding annealing at 850° C.for 50 hours to develop secondary recrystallized grains strongly alignedin Goss orientation and subjected to purification annealing in dry H₂ of1200° C.

The surface of thus obtained grain oriented silicon steel sheet issmoothened through chemical polishing after the removal of oxide filmfrom the surface of the silicon steel sheet. Further, Si is formed at athickness of 0.05 μm by a magnetron sputtering method and treated in amixed gas of N₂(50%)+H₂(50%) at 1000° C. for 15 minutes. Thereafter, atension insulating film (thickness of about 2 μm) consisting essentiallyof colloidal silica and phosphate is formed on the surface of the steelsheet and baked at 800° C.

The magnetic properties and adhesion property in the thus obtainedproduct are as follows.

Magnetic properties B₈ : 1.88 T W_(17/50): 0.66 W/kg Adhesion propertygood without peeling by 180° bending on a round rod of diameter: 20 mm

And also, an extremely thin Si-containing nitride-oxide layer is formedon the surface of as-pickled steel sheet without chemical polishing andthen a tension insulating film of a phosphate is formed thereon. Themagnetic properties and adhesion property in the thus obtained productare as follows.

Magnetic properties B₈: 1.88 T W_(17/50): 0.68 W/kg Adhesion propertygood without peeling by 180° bending on a round rod of diameter: 20 mm

EXAMPLE 4

A continuously cast slab of silicon steel having a composition of C:0.073 wt %, Si: 3.38 wt %, Mn: 0.078 wt %, Se: 0.020 wt %, Sb: 0.025 wt%, Al: 0.020 wt %, N: 0.0077 wt % and Mo: 0.012 wt % and the remainderbeing substantially Fe is heated at 1340° C. for 5 hours and hot rolledto obtain a hot rolled sheet of thickness: 2.3 mm. Then, the hot rolledsheet is subjected to normalization annealing at 1000° C. and coldrolled twice through an intermediate annealing at 1050° C. to obtain afinal cold rolled sheet of thickness: 0.23 mm.

After the decarburization and primary recrystallization annealing in wetH₂ of 840° C., a slurry of an annealing separator having a compositionof MgO(20%), Al₂O₃(50%), CaSiO₃(10%) and PbCl₂(20%) is applied to thesurface of the steel sheet and annealed at 850° C. for 15 hours andtemperature is raised from 850° C. to 1180° C. at a rate of 12° C./h todevelop secondary recrystallized grains strongly aligned in Gossorientation and subjected to purification annealing in dry H₂ of 1220°C.

The thus obtained silicon steel sheet is subjected to {circle around(1)} a smoothening treatment through chemical polishing or {circlearound (2)} a pickling treatment with 10% HCl after the removal of oxidefilm from the surface.

Then, the silicon steel sheet is immersed in an aqueous solution (85°C.) of SiCl₄ (0.2 mol/l) for 0.5 minute and thereafter a treatingsolution for an insulating coating consisting essentially of a phosphateand chromic acid and further a treating solution for tension insulatingcoating consisting essentially of colloidal silica and a phosphate areapplied and baked at 800° C. to form a two-layer tension insulating filmhaving a total thickness: about 2.0 μm (0.5 μm+1.5 μm).

The magnetic properties and adhesion property in the thus obtainedproduct are as follows.

{circle around (1)} In case of the smoothening treatment

Magnetic properties B₈: 1.94 T W_(17/50): 0.71 W/kg Adhesion propertygood without peeling by 180° bending on a round rod of diameter: 20 mm

{circle around (2)} In case of the pickling treatment

Magnetic properties B₈: 1.94 T W_(17/50): 0.73 W/kg Adhesion propertygood without peeling by 180° bending on a round rod of diameter: 20 mm

EXAMPLE 5

A continuously cast slab of silicon steel having a composition of C:0.076 wt %, Si: 3.41 wt %, Mn: 0.078 wt %, Se: 0.020 wt %, Sb: 0.025 wt%, Al: 0.020 wt %, N: 0.0072 wt % and Mo: 0.012 wt % and the remainderbeing substantially Fe is heated at 1340° C. for 5 hours and hot rolledto obtain a hot rolled sheet of thickness: 2.0 mm. The hot rolled sheetis subjected to normalization annealing at 950° C. and cold rolled twicethrough an intermediate annealing at 1050° C. to obtain a final coldrolled sheet of thickness: 0.23 mm.

Then, an etching resist ink consisting essentially of an alkyd resin isapplied onto the surface of the final cold rolled sheet by gravureoffset printing so as to leave linear non-coated portions of width: 200μm at an interval: 4 mm in a direction substantially perpendicular to arolling direction, and baked at 200° C. for about 20 seconds. In thiscase, a resist thickness is 2 μm. The steel sheet coated with theetching resist is subjected to an electrolytic etching to form lineargrooves of width: 200 μm and depth: 20 μm and then immersed in anorganic solvent to remove the resist. In this case, the electrolyticetching is carried out in NaCl electrolyte under conditions of currentdensity: 10 A/dm² and treating time: 20 seconds.

After the decarburization and primary recrystallization annealing in wetH₂ of 840° C., a slurry of an annealing separator having a compositionof MgO(25%), Al₂O₃(70%) and CaSiO₃(5%) is applied to the surface of thesteel sheet and annealed at 850° C. for 15 hours and temperature israised from 850° C. to 1150° C. at a rate of 10° C./h to developsecondary recrystallized grains strongly aligned in Goss orientation andsubjected to purification annealing in dry H₂ of 1200° C.

The surface of thus obtained grain oriented silicon steel sheet issmoothened through chemical polishing after the removal of oxide filmfrom the surface of the silicon steel sheet.

Then, the silicon steel sheet is immersed in an aqueous solution (90°C.) of SiCl₄ (0.8 mol/l) for 10 seconds in a vacuum glow box whileflowing N₂ gas into the box and then subjected to an exposure treatmentin a nitrogen atmosphere for 5 seconds. After this method is repeatedthree times, a tension insulating film (thickness of about 2 μm)consisting essentially of colloidal silica and phosphate is formed onthe surface of the steel sheet and baked at 820° C.

The magnetic properties and adhesion property in the thus obtainedproduct are as follows.

Magnetic properties B₈: 1.91 T W_(17/50): 0.58 W/kg Adhesion propertygood without peeling by 180° bending on a round rod of diameter: 20 mm

EXAMPLE 6

A continuously cast slab of silicon steel having a composition of C:0.076 wt %, Si: 3.38 wt %, Mn: 0.069 wt %, Se: 0.020 wt %, Sb: 0.025 wt%, Al: 0.021 wt %, N: 0.0076 wt % and Mo: 0.012 wt % and the remainderbeing substantially Fe is heated at 1360° C. for 5 hours and hot rolledto obtain a hot rolled sheet of thickness: 2.2 mm. Then, the hot rolledsheet is subjected to normalization annealing at 1000° C. and coldrolled twice through an intermediate annealing at 1050° C. to obtain afinal cold rolled sheet of thickness: 0.23 mm.

After the decarburization and primary recrystallization annealing in wetH₂ of 850° C., a slurry of an annealing separator having a compositionof MgO(20%), Al₂O₃(70%) and CaSiO₃(10%) is applied to the surface of thesteel sheet and annealed at 850° C. for 15 hours and temperature israised from 850° C. to 1180° C. at a rate of 10° C./h to developsecondary recrystallized grains strongly aligned in Goss orientation andsubjected to purification annealing in dry H₂ of 1200° C.

The thus obtained silicon steel sheet is subjected to a {circle around(1)} a smoothening treatment through chemical polishing or {circlearound (2)} a pickling treatment with 10% HCl after the removal of oxidefilm from the surface.

Then, the silicon steel sheet is immersed in a treating solution (80°C.) obtained by diluting 250 cc of a coating solution for tensioninsulating film consisting essentially of magnesium phosphate andcolloidal silica with 1500 cc of a distilled water and adding SiCl₄: 20cc, FeCl₃: 20 g and Al(NO₃)₃: 10 g to the diluted solution for 20seconds and treated in a mixed gas of N₂(50%)+H₂(50%) at 950° C. for 7minutes to form an extremely thin base film having a thickness: 0.2 μm.Thereafter, a tension insulating film (thickness of about 2 μm)consisting essentially of colloidal silica and phosphate is formed onthe surface of the steel sheet and baked at 800° C.

The magnetic properties, adhesion property and compression stressproperty of magnetostriction in the thus obtained product are asfollows.

{circle around (1)} In case of the smoothening treatment

Magnetic properties B₈: 1.94 T W_(17/50): 0.64 W/kg Adhesion propertygood without peeling by 180° bending on a round rod of diameter: 25 mmMagnetostriction magnetic strain λ_(PP) = 0.8 × 10⁻⁶ at compressionstress σ = 0.4 kg/mm², magnetic strain λ_(PP) = 0.9 × 10⁻⁶ atcompression stress σ = 0.6 kg/mm²

{circle around (2)} In case of the pickling treatment

Magnetic properties B₈: 1.93 T W_(17/50): 0.68 W/kg Adhesion propertygood without peeling by 180° bending on a round rod of diameter: 25 mmMagnetostriction magnetic strain λ_(PP) = 0.7 × 10⁻⁶ at compressionstress σ = 0.4 kg/mm², magnetic strain λ_(PP) = 0.9 × 10⁻⁶ atcompression stress σ = 0.6 kg/mm²

After the above product sheet is subjected to a strain relief annealingat 800° C. for 3 hours, the magnetic properties are measured. As aresult, the degradation of the properties is not observed in both cases{circle around (1)} and {circle around (2)} as shown below.

{circle around (1)} Magnetic properties B₈: 1.94 T W_(17/50): 0.64 W/kg{circle around (2)} Magnetic properties B₈: 1.93 T W_(17/50): 0.68 W/kg

For the comparison, after the decarburization and primaryrecrystallization annealing in wet H₂ of 840° C., a slurry of anannealing separator mainly composed of MgO is applied to the surface ofthe steel sheet and annealed at 850° C. for 15 hours and temperature israised from 850° C. to 1180° C. at a rate of 10° C./h to developsecondary recrystallized grains strongly aligned in Goss orientation andsubjected to purification annealing in dry H₂ of 1200° C. Thereafter, atension insulating film (thickness of about 2 μm) consisting essentiallyof colloidal silica and phosphate is formed on a forsterite base filmand baked at 800° C. The magnetic properties, adhesion property andcompression stress property of magnetostriction in the thus obtainedgrain oriented silicon steel sheet are measured to obtain results asfollows.

Magnetic properties B₈: 1.94 T W_(17/50): 0.76 W/kg Adhesion property nopeeling by 180° bending on a round rod of diameter: 20 mmMagnetostriction magnetic strain λ_(PP) = 1.6 × 10⁻⁶ at compressionstress σ = 0.4 kg/mm², magnetic strain λ_(PP) = 4.8 × 10⁻⁶ atcompression stress σ = 0.6 kg/mm²

EXAMPLE 7

A continuously cast slab of silicon steel having a composition of C:0.069 wt %, Si: 3.42 wt %, Mn: 0.073 wt %, Se: 0.020 wt %, Sb: 0.023 wt%, Al: 0.020 wt %, N: 0.0072 wt % and Mo: 0.013 wt % and the remainderbeing substantially Fe is heated at 1360° C. for 4 hours and hot rolledto obtain a hot rolled sheet of thickness: 2.0mm. The hot rolled sheetis subjected to normalization annealing at 980° C. and cold rolled twicethrough an intermediate annealing at 1050° C. to obtain a final coldrolled sheet of thickness: 0.23 mm.

Then, an etching resist ink consisting essentially of an alkyd resin isapplied onto the surface of the final cold rolled sheet by gravureoffset printing so as to leave linear non-coated portions of width: 200μm at an interval: 4 mm in a direction substantially perpendicular to arolling direction, and baked at 200° C. for about 20 seconds. In thiscase, a resist thickness is 2 μm. The steel sheet coated with theetching resist is subjected to an electrolytic etching to form lineargrooves of width: 200 μm and depth: 20 μm and then immersed in anorganic solvent to remove the resist. In this case, the electrolyticetching is carried out in NaCl electrolyte under conditions of currentdensity: 10 A/dm² and treating time: 20 seconds.

After the decarburization and primary recrystallization annealing in wetH₂ of 850° C., a slurry of an annealing separator having a compositionof MgO(20%), Al₂O₃(70%) and CaSiO₃(10%) is applied to the surface of thesteel sheet and annealed at 850° C. for 15 hours and temperature israised from 850° C. to 1150° C. at a rate of 12° C./h to developsecondary recrystallized grains strongly aligned in Goss orientation andsubjected to purification annealing in dry H₂ of 1200° C.

The surface of thus obtained grain oriented silicon steel sheet issmoothened through chemical polishing after the removal of oxide filmfrom the surface of the silicon steel sheet.

Then, the silicon steel sheet is immersed in an aqueous solution ofSiCl₄: 20 cc dissolved in 1500 cc of water at 80° C. for 10 seconds andtreated in a mixed gas of N₂(50%)+H₂(50%) at 950° C. for 3 minutes.Thereafter, it is immersed in a treating solution (80° C.) obtained bydiluting 250 cc of a coating solution for tension insulating filmconsisting essentially of magnesium phosphate and colloidal silica with1500 cc of a distilled water and adding SiCl₄: 20 cc, AlPO₄: 15 g andH₃BO₃: 19 g to the diluted solution for 20 seconds and treated in amixed gas of N₂(93%)+H₂(7%) at 900° C. for 10 minutes to form anextremely thin base film having a thickness: 0.4 μm. Thereafter, atension insulating film (thickness of about 2 μm) consisting essentiallyof colloidal silica and phosphate is formed on the surface of the steelsheet and baked at 800° C.

The magnetic properties and adhesion property in the thus obtainedproduct are as follows.

Magnetic properties B₈: 1.91 T W_(17/50): 0.57 W/kg Adhesion propertygood without peeling by 180° bending on a round rod of diameter: 20 mm

After the above product sheet is subjected to a strain relief annealingat 800° C. for 3 hours, the magnetic properties are examined to obtainresults as follows:

Magnetic properties B₈: 1.91 T W_(17/50): 0.57 W/kg

There is not observed the degradation of the magnetic properties throughthe strain relief annealing.

And also, the as-pickled steel sheet without chemical polishing isimmersed in a treating solution (80° C.) obtained by diluting 250 cc ofa coating solution for tension insulating film consisting essentially ofmagnesium phosphate and colloidal silica with 1500 cc of a distilledwater and adding SiCl₄: 20 cc, AlPO₄: 15 g and H₃BO₃: 19 g to thediluted solution for 20 seconds and treated in a mixed gas ofN₂(93%)+H₂(7%) at 900° C. for 10 minutes in the same manner as describedabove. Thereafter, the tension insulating film is formed thereon. Themagnetic properties and adhesion property in the thus obtained productare as follows.

Magnetic properties B₈: 1.91 T W_(17/50): 0.65 W/kg Adhesion propertygood without peeling by 180° bending on a round rod of diameter: 20 mm

With respect to this product, the magnetic properties are examined afterthe strain relief annealing at 800° C. for 3 hours to obtain results asfollows:

Magnetic properties B₈: 1.91 T W_(17/50): 0.65 W/kg

There is not observed the degradation of the magnetic properties throughthe strain relief annealing.

EXAMPLE 8

A continuously cast slab of silicon steel having a composition of C:0.042 wt %, Si: 3.46 wt %, Mn: 0.070 wt %, Se: 0.021 wt %, Sb: 0.025 wt% and Mo: 0.012 wt % and the remainder being substantially Fe is heatedat 1340° C. for 4 hours and hot rolled to obtain a hot rolled sheet ofthickness: 2.4 mm. The hot rolled sheet is subjected to normalizationannealing at 900° C. and cold rolled twice through an intermediateannealing at 950° C. to obtain a final cold rolled sheet of thickness:0.23 mm.

Then, an etching resist ink consisting essentially of an alkyd resin isapplied onto the surface of the final cold rolled sheet by gravureoffset printing so as to leave linear non-coated portions of width: 200μm at an interval: 4 mm in a direction substantially perpendicular to arolling direction, and baked at 200° C. for about 20 seconds. In thiscase, a resist thickness is 2 μm. The steel sheet coated with theetching resist is subjected to an electrolytic etching to form lineargrooves of width: 200 μm and depth: 20 μm and then immersed in anorganic solvent to remove the resist. In this case, the electrolyticetching is carried out in NaCl electrolyte under conditions of currentdensity: 10 A/dm² and treating time: 20 seconds.

After the decarburization and primary recrystallization annealing in wetH₂ of 840° C., a slurry of an annealing separator having a compositionof MgO(25%), Al₂O₃(70%) and CaSiO₃(5%) is applied to the surface of thesteel sheet and subjected to a temperature-holding annealing at 850° C.for 50 hours to develop secondary recrystallized grains strongly alignedin Goss orientation and subjected to purification annealing in dry H₂ of1200° C.

The surface of thus obtained grain oriented silicon steel sheet issmoothened through chemical polishing after the removal of oxide filmfrom the surface of the silicon steel sheet. Further, the silicon steelsheet is immersed in a treating solution (80° C.) obtained by diluting250 cc of a coating solution for tension insulating film consistingessentially of aluminum phosphate and colloidal silica with 1500 cc of adistilled water and adding SiCl₄: 50 cc to the diluted solution for 20seconds and treated in a mixed gas of N₂(50%)+H₂(50%) at 950° C. for 10minutes to form an extremely thin base film having a thickness: 0.6 μm.Thereafter, a tension insulating film (thickness of about 2 μm)consisting essentially of colloidal silica and aluminum phosphate isformed on the surface of the steel sheet and baked at 800° C.

The magnetic properties and adhesion property in the thus obtainedproduct are as follows.

Magnetic properties B₈: 1.88 T W_(17/50): 0.63 W/kg Adhesion propertygood without peeling by 180° bending on a round rod of diameter: 25 mm

And also, the extremely thin tension film finely dispersed with an oxideof Si is formed on the surface of the as-pickled steel sheet withoutchemical polishing in the same manner as described above and thereafterthe tension insulating film of aluminum phosphate is formed thereon. Themagnetic properties and adhesion property in the thus obtained productare as follows.

Magnetic properties B₈: 1.88 T W_(17/50): 0.67 W/kg Adhesion propertygood without peeling by 180° bending on a round rod of diameter: 20 mm

With respect to this product, the magnetic properties are examined afterthe strain relief annealing at 800° C. for 3 hours to obtain results asfollows:

In case of the smoothening treatment

Magnetic properties B₈: 1.88 T W_(17/50): 0.63 W/kg

In case of the pickling treatment

Magnetic properties B₈: 1.88 T W_(17/50): 0.67 W/kg

EXAMPLE 9

A continuously cast slab of silicon steel having a composition of C:0.073 wt %, Si: 3.40 wt %, Mn: 0.072 wt %, Se: 0.020 wt %, Sb: 0.023 wt%, Al: 0.019 wt %, N: 0.0074 wt % and Mo: 0.013 wt % and the remainderbeing substantially Fe is heated at 1340° C. for 5 hours and hot rolledto obtain a hot rolled sheet of thickness: 2.0 mm. The hot rolled sheetis subjected to normalization annealing at 1000° C. and cold rolledtwice through an intermediate annealing at 1050° C. to obtain a finalcold rolled sheet of thickness: 0.23 mm.

Then, an etching resist ink consisting essentially of an alkyd resin isapplied onto the surface of the final cold rolled sheet by gravureoffset printing so as to leave linear non-coated portions of width: 200μm at an interval: 4 mm in a direction substantially perpendicular to arolling direction, and baked at 200° C. for about 20 seconds. In thiscase, a resist thickness is 2 μm. The steel sheet coated with theetching resist is subjected to an electrolytic etching to form lineargrooves of width: 200 μm and depth: 20 μm and then immersed in anorganic solvent to remove the resist. In this case, the electrolyticetching is carried out in NaCl electrolyte under conditions of currentdensity: 10 A/dm² and treating time: 20 seconds.

After the decarburization and primary recrystallization annealing in wetH₂ of 840° C., a slurry of an annealing separator having a compositionof MgO(20%), Al₂O₃(70%) and CaSiO₃(10%) is applied to the surface of thesteel sheet and annealed at 850° C. for 15 hours and temperature israised from 850° C. to 1100° C. at a rate of 12° C./h to developsecondary recrystallized grains strongly aligned in Goss orientation andsubjected to purification annealing in dry H₂ of 1200° C.

The surface of thus obtained grain oriented silicon steel sheet issmoothened through chemical polishing after the removal of oxide filmfrom the surface of the silicon steel sheet.

Then, the silicon steel sheet is immersed in an aqueous solution ofSiCl₄: 25 cc and AlNO₃: 5 g in 1500 cc of water at 90° C. for 40seconds. Thereafter, it is immersed in a treating solution (80° C.)obtained by diluting 250 cc of a coating solution for tension insulatingfilm consisting essentially of magnesium phosphate and colloidal silicawith 1500 cc of a distilled water and adding SiCi₄: 20 cc, AlPO₄: 15 gand H₃BO₃: 10 g to the diluted solution for 20 seconds. Further, atension insulating film (thickness of about 1.5 μm) consistingessentially of colloidal silica and magnesium phosphate is formed on thesurface of the steel sheet and baked at 800° C.

The magnetic properties and adhesion property in the thus obtainedproduct are as follows.

Magnetic properties B₈: 1.91 T W_(17/50): 0.59 W/kg Adhesion propertygood without peeling by 180° bending on a round rod of diameter: 20 mm

EXAMPLE 10

A continuously cast slab of silicon steel having a composition of C:0.078 wt %, Si: 3.36 wt %, Mn: 0.070 wt %, Se: 0.019 wt %, Sb: 0.022 wt%, Al: 0.019 wt %, N: 0.0076 wt % and Mo: 0.012 wt % and the remainderbeing substantially Fe is heated at 1340° C. for 5 hours and hot rolledto obtain a hot rolled sheet of thickness: 2.2 mm. Then, the hot rolledsheet is subjected to normalization annealing at 950° C. and cold rolledtwice through an intermediate annealing at 1000° C. to obtain a finalcold rolled sheet of thickness: 0.23 mm.

After the decarburization and primary recrystallization annealing in wetH₂ of 840° C., a slurry of an annealing separator having a compositionof CaO(20%), Al₂O₃(40%) and SiO₂(40%) is applied to the surface of thesteel sheet and annealed at 850° C. for 15 hours and temperature israised from 850° C. to 1100° C. at a rate of 10° C./h to developsecondary recrystallized grains strongly aligned in Goss orientation andsubjected to purification annealing in dry H₂ of 1200° C.

The thus obtained silicon steel sheet is subjected to {circle around(1)} a smoothening treatment through chemical polishing or {circlearound (2)} a pickling treatment with 10% HCl after the removal of oxidefilm from the surface.

Then, the silicon steel sheet is immersed in an aqueous solution ofSiCl₄ solution: 20 cc and SiO₂: 5 g in 1500 cc of a distilled water at80° C. for 20 seconds and subjected to a heat treatment in a mixed gasof N₂(50%)+H₂(50%) at 900° C. for 5 minutes.

Thereafter, it is immersed in a treating solution (80° C.) obtained bydiluting 250 cc of a coating solution for tension insulating filmconsisting essentially of magnesium phosphate and colloidal silica with1500 cc of a distilled water and adding SiCl₄: 20 cc, AlPO₄: 10 g andH₃BO₄: 10 g to the diluted solution for 20 seconds. In this case, theweight reduction is about 0.06 g or the sheet thickness decreased amountis about 1.2 μm. Then, it is subjected to a heat treatment in a mixedgas of N₂(93%)+H₂(7%) at 900° C. for 5 minutes to form a base filmhaving a thickness: 0.3 μm.

Thereafter, a coating solution for tension insulating film consistingessentially of colloidal silica and magnesium phosphate is coated ontothe surface of the steel sheet, dried and baked at 800° C. to form atension insulating film having a thickness: 2 μm.

The magnetic properties, adhesion property and compression stressproperty of magnetostriction in the thus obtained product are asfollows.

{circle around (1)} In case of smoothening treatment

Magnetic properties B₈: 1.93 T W_(17/50): 0.64 W/kg Adhesion propertygood without peeling by 180° bending on a round rod of diameter: 15 mmMagnetostriction magnetic strain λ_(pp) 0.8 × 10⁻⁶ at compression stressσ = 0.4 kg/mm², magnetic strain λ_(pp) = 1.1 × 10⁻⁶ at compressionstress σ = 0.6 kg/mm²

{circle around (2)} In case of the pickling treatment

Magnetic properties B₈: 1.92 T W_(17/50): 0.67 W/kg Adhesion propertygood without peeling by 180° bending on a round rod of diameter: 15 mmMagnetostriction magnetic strain λ_(pp) = 0.9 × 10⁻⁶ at compressionstress σ = 0.4 kg/mm², magnetic strain λ_(pp) = 1.2 × 10⁻⁶ atcompression stress σ = 0.6 kg/mm²

EXAMPLE 11

A continuously cast slab of silicon steel having a composition of C:0.072 wt %, Si: 3.36 wt %, Mn: 0.071 wt %, Se: 0.019 wt %, Sb: 0.023 wt%, Al: 0.019 wt %, N: 0.0073 wt % and Mo: 0.013 wt % and the remainderbeing substantially Fe is heated at 1360° C. for 5 hours and hot rolledto obtain a hot rolled sheet of thickness: 2.0 mm. The hot rolled sheetis subjected to normalization annealing at 1000° C. and cold rolledtwice through an intermediate annealing at 1000° C. to obtain a finalcold rolled sheet of thickness: 0.23 mm.

Then, an etching resist ink consisting essentially of an alkyd resin isapplied onto the surface of the final cold rolled sheet by gravureoffset printing so as to leave linear non-coated portions of width: 200μm at an interval: 4 mm in a direction substantially perpendicular to arolling direction, and baked at 200° C. for about 20 seconds. In thiscase, a resist thickness is 2 μm. The steel sheet coated with theetching resist is subjected to an electrolytic etching to form lineargrooves of width: 200 μm and depth: 20 μm and then immersed in anorganic solvent to remove the resist. In this case, the electrolyticetching is carried out in NaCl electrolyte under conditions of currentdensity: 10 A/dm² and treating time: 20 seconds.

After the decarburization and primary recrystallization annealing in wetH₂ of 850° C., a slurry of an annealing separator having a compositionof MgO(5%), CaO(25%), Al₂O₃(30%), CaSiO₃(10%) and SiO₂(30%) is appliedto the surface of the steel sheet and annealed at 850° C. for 15 hoursand temperature is raised from 850° C. to 1050° C. at a rate of 12° C./hto develop secondary recrystallized grains strongly aligned in Gossorientation and subjected to purification annealing in dry H₂ of 1200°C.

The surface of thus obtained grain oriented silicon steel sheet issmoothened through chemical polishing after the removal of oxide filmfrom the surface of the silicon steel sheet.

Then, the silicon steel sheet is immersed in an aqueous solution ofSiCl₄: 15 cc and FeCl₃: 10 g in 1500 cc of a distilled water at 85° C.for 10 seconds and treated in a mixed gas of N₂(50%)+H₂(50%) at 950° C.

Thereafter, it is immersed in a treating solution (80° C.) obtained bydiluting 250 cc of a coating solution for tension insulating filmconsisting essentially of magnesium phosphate and colloidal silica with1500 cc of a distilled water and adding SiCl₄: 25 cc, AlCl₃: 5 g andH₃BO₄: 10 g to the diluted solution for 20 seconds. In this case, theweight reduction is about 0.04 g or the sheet thickness decreased amountis about 0.8 μm. Then, it is subjected to a heat treatment in a mixedgas of N₂(93%)+H₂(7%) at 900° C. for 10 minutes to form a base filmhaving a thickness: 0.2 μm.

Thereafter, a coating solution for tension insulating film consistingessentially of colloidal silica and magnesium phosphate is coated ontothe surface of the steel sheet, dried and baked at 800° C. to form atension insulating film having a thickness: about 1.5 μm.

The magnetic properties and adhesion property in the thus obtainedproduct are as follows.

Magnetic properties B₈: 1.90 T W_(17/50): 0.58 W/kg Adhesion propertygood without peeling by 180° bending on a round rod of diameter: 10 mm

And also, the pretreatment, treatment for the formation of base film andtreatment for the formation of tension insulating film are carried outon the surface of the as-pickled steel sheet without chemical polishingunder the same conditions as mentioned above. The magnetic propertiesand adhesion property in the thus obtained product are as follows.

Magnetic properties B₈: 1.90 T W_(17/50): 0.64 W/kg Adhesion propertygood without peeling by 180° bending on a round rod of diameter: 10 mm

EXAMPLE 12

A continuously cast slab of silicon steel having a composition of C:0.042 wt %, Si: 3.36 wt %, Mn: 0.068 wt %, Se: 0.022 wt %, Sb: 0.025 wt% and Mo: 0.012 wt % and the remainder being substantially Fe is heatedat 1330° C. for 4 hours and hot rolled to obtain a hot rolled sheet ofthickness: 2.4 mm. The hot rolled sheet is subjected to normalizationannealing at 950° C. and cold rolled twice through an intermediateannealing at 980° C. to obtain a final cold rolled sheet of thickness:0.23 mm.

Then, an etching resist ink consisting essentially of an alkyd resin isapplied onto the surface of the final cold rolled sheet by gravureoffset printing so as to leave linear non-coated portions of width: 200μm at an interval: 4 mm in a direction substantially perpendicular to arolling direction, and baked at 200° C. for about 20 seconds. In thiscase, a resist thickness is 2 μm. The steel sheet coated with theetching resist is subjected to an electrolytic etching to form lineargrooves of width: 200 μm and depth: 20 μm and then immersed in anorganic solvent to remove the resist. In this case, the electrolyticetching is carried out in NaCl electrolyte under conditions of currentdensity: 10 A/dm² and treating time: 20 seconds.

After the decarburization and primary recrystallization annealing in wetH₂ of 840° C., a slurry of an annealing separator having a compositionof MgO(5%), Al₂O₃(50%), CaSiO₃(5%) and SiO₂(40%) is applied to thesurface of the steel sheet and subjected to temperature-holdingannealing at 850° C. for 50 hours to develop secondary recrystallizedgrains strongly aligned in Goss orientation and subjected topurification annealing in dry H₂ of 1200° C.

The surface of thus obtained grain oriented silicon steel sheet issmoothened through chemical polishing after the removal of oxide filmfrom the surface of the silicon steel sheet.

Then, the silicon steel sheet is immersed in an aqueous solution ofSiCl₄: 15 cc dissolved in 1500 cc of a distilled water at 90° C. for 15seconds and treated in a mixed gas of N₂(50%)+H₂(50%) at 900° C.

Thereafter, it is immersed in a treating solution (80° C.) obtained bydiluting 100 cc of a coating solution for tension insulating filmconsisting essentially of aluminum phosphate and colloidal silica with1500 cc of a distilled water and adding SiCl₄: 15 cc, AlCl₃: 5 g andH₃BO₃: 5 g to the diluted solution for 15 seconds. In this case, theweight reduction is about 0.08 g or the sheet thickness decreased amountis about 1.6 μm. Then, it is treated in a mixed gas of N₂(93%)+H₂(7%) at880° C. for 3 minutes to form a base film having a thickness: 0.4 μm.

Thereafter, a coating solution for tension insulating film consistingessentially of colloidal silica and phosphate is coated onto the surfaceof the steel sheet, dried and baked at 800° C. to form a tensioninsulating film having a thickness: about 2.5 μm.

The magnetic properties and adhesion property in the thus obtainedproduct are as follows.

Magnetic properties B₈: 1.88 T W_(17/50): 0.63 W/kg Adhesion propertygood without peeling by 180° bending on a round rod of diameter: 15 mm

After the above product sheet is subjected to a strain relief annealingat 800° C. for 3 hours, the magnetic properties are examined to obtainresults as follows:

Magnetic properties B₈: 1.88 T W_(17/50): 0.61 W/kg

There is not observed the degradation of the magnetic properties throughthe strain relief annealing.

And also, the pretreatment, treatment for the formation of base film andtreatment for the formation of tension insulating film are carried outon the surface of the as-pickled steel sheet without chemical polishingunder the same conditions as mentioned above. The magnetic propertiesand adhesion property in the thus obtained product are as follows.

Magnetic properties B₈: 1.88 T W_(17/50): 0.67 W/kg Adhesion propertygood without peeling by 180° bending on a round rod of diameter: 10 mm

EXAMPLE 13

A continuously cast slab of silicon steel having a composition of C:0.074 wt %, Si: 3.31 wt %, Mn: 0.076 wt %, Se: 0.020 wt %, Sb: 0.023 wt%, Al: 0.020 wt %, N: 0.0071 wt % and Mo: 0.012 wt % and the remainderbeing substantially Fe. is heated at 1340° C. for 5 hours and hot rolledto obtain a hot rolled sheet of thickness: 2.0 mm. The hot rolled sheetis subjected to normalization annealing at 1000° C. and cold rolledtwice through an intermediate annealing at 1000° C. to obtain a finalcold rolled sheet of thickness: 0.23 mm.

Then, an etching resist ink consisting essentially of an alkyd resin isapplied onto the surface of the final cold rolled sheet by gravureoffset printing so as to leave linear non-coated portions of width: 200μm at an interval: 4 mm in a direction substantially perpendicular to arolling direction, and baked at 200° C. for about 20 seconds. In thiscase, a resist thickness is 2 μm. The steel sheet coated with theetching resist is subjected to an electrolytic etching to form lineargrooves of width: 200 μm and depth: 20 μm and then immersed in anorganic solvent to remove the resist. In this case, the electrolyticetching is carried out in NaCl electrolyte under conditions of currentdensity: 10 A/dm² and treating time: 20 seconds.

After the decarburization and primary recrystallization annealing in wetH₂ of 850° C., a slurry of an annealing separator having a compositionof MgO(5%), CaO(25%), Al₂O₃(30%), CaSiO₃(10%), SiO₂(30%) and PbCl₂(20%)is applied to the surface of the steel sheet and annealed at 850° C. for15 hours and temperature is raised from 850° C. to 1050° C. at a rate of12° C./h to develop secondary recrystallized grains strongly aligned inGoss orientation and subjected to purification annealing in dry H₂ of1200° C.

The surface of thus obtained grain oriented silicon steel sheet issmoothened through chemical polishing after the removal of oxide filmfrom the surface of the silicon steel sheet.

Then, the silicon steel sheet is immersed in an aqueous solution ofSiCl₄: 15 cc and FeCl₃: 5 g dissolved in 1500 cc of a distilled water at85° C. for 10 seconds.

Thereafter, it is immersed in a treating solution (80° C.) obtained bydiluting 250 cc of a coating solution for tension insulating filmconsisting essentially of magnesium phosphate and colloidal silica with1500 cc of a distilled water and adding SiCl₄: 15 cc, AlCl₃: 5 g andH₃BO₄: 5 g to the diluted solution for 20 seconds. In this case, theweight reduction is about 0.02 g or the sheet thickness decreased amountis about 0.4 μm.

Then, a coating solution for insulating film consisting essentially ofmagnesium phosphate and chromic acid is applied at a thickness of 0.5 μmand further a coating solution for tension insulating film consistingessentially of colloidal silica and magnesium phosphate is coatedthereon, dried and baked at 800° C. to form a tension insulating filmhaving a thickness: about 1.0 μm.

The magnetic properties and adhesion property in the thus obtainedproduct are as follows.

Magnetic properties B₈: 1.91 T W_(17/50): 0.63 W/kg Adhesion propertygood without peeling by 180° bending on a round rod of diameter: 10 mm

And also, the pretreatment, treatment for the formation of base film andtreatment for the formation of tension insulating film are carried outon the surface of the as-pickled steel sheet without chemical polishingunder the same conditions as mentioned above. The magnetic propertiesand adhesion property in the thus obtained product are as follows.

Magnetic properties B₈: 1.91 T W_(17/50): 0.67 W/kg Adhesion propertygood without peeling by 180° bending on a round rod of diameter: 10 mm

EXAMPLE 14

A continuously cast slab of silicon steel having a composition of C:0.076 wt %, Si: 3.41 wt %, Mn: 0.078 wt %, Se: 0.019 wt %, Sb: 0.025 wt%, Al: 0.020 wt %, N: 0.0076 wt % and Mo: 0.012 wt % and the remainderbeing substantially Fe is heated at 1350° C. for 4 hours and hot rolledto obtain a hot rolled sheet of thickness: 2.0 mm. The hot rolled sheetis subjected to normalization annealing at 1000° C. and cold rolledtwice through an intermediate annealing at 1020° C. to obtain a finalcold rolled sheet of thickness: 0.23 mm.

Then, an etching resist ink consisting essentially of an alkyd resin isapplied onto the surface of the final cold rolled sheet by gravureoffset printing so as to leave linear non-coated portions of width: 200μm at an interval: 4 mm in a direction substantially perpendicular to arolling direction, and baked at 200° C. for about 20 seconds. In thiscase, a resist thickness is 2 μm. The steel sheet coated with theetching resist is subjected to an electrolytic etching to form lineargrooves of width: 200 μm and depth: 20 μm and then immersed in anorganic solvent to remove the resist. In this case, the electrolyticetching is carried out in NaCl electrolyte under conditions of currentdensity: 10 A/dm² and treating time: 20 seconds.

After the decarburization and primary recrystallization annealing in wetH₂ of 840° C., a slurry of an annealing separator having a compositionof MgO(5%), CaO(25%), Al₂O₃(30%), CaSiO₃(10%) and SiO₂(30%) is appliedto the surface of the steel sheet and annealed at 850° C. for 15 hoursand temperature is raised from 850° C. to 1050° C. at a rate of 12° C./hto develop secondary recrystallized grains strongly aligned in Gossorientation and subjected to purification annealing in dry H₂ of 1200°C.

The surface of thus obtained grain oriented silicon steel sheet issmoothened through chemical polishing after the removal of oxide filmfrom the surface of the silicon steel sheet.

Then, the silicon steel sheet is treated in a vacuum glow box in N₂ gasatmosphere. That is, the silicon steel sheet is immersed in an aqueoussolution of SiCl₄: 25 cc and AlNO₃: 5 g dissolved in 1500 cc of adistilled water at 90° C. for 10 seconds and then exposed in N₂ gasatmosphere for 5 seconds. This treatment is repeated three times.

Thereafter, it is immersed in a treating solution (80° C.) obtained bydiluting 250 cc of a coating solution for tension insulating filmconsisting essentially of magnesium phosphate and colloidal silica with1500 cc of a distilled water and adding SiCl₄: 25 cc, AlCl₃: 5 g andH₃BO₄: 10 g to the diluted solution for 20 seconds. In this case, theweight reduction is about 0.04 g or the sheet thickness decreased amountis about 0.8 μm. Then, a coating solution for tension insulating filmconsisting essentially of colloidal silica and magnesium phosphate iscoated on the surface of the steel sheet, dried and baked at 800° C. toform a tension insulating film having a thickness: about 1.5 μm.

The magnetic properties and adhesion property in the thus obtainedproduct are as follows.

Magnetic properties B₈: 1.90 T W_(17/50): 0.57 W/kg Adhesion propertygood without peeling by 180° bending on a round rod of diameter: 20 mm

EXAMPLE 15

A continuously cast slab of silicon steel having a composition of C:0.075 wt %, Si: 3.47 wt %, Mn: 0.068 wt %, Se: 0.020 wt %, Sb: 0.025 wt%, Al: 0.020 wt %, N: 0.0073 wt % and Mo: 0.012 wt % and the remainderbeing substantially Fe is heated at 1350° C. for 5 hours and hot rolledto obtain a hot rolled sheet of thickness: 2.2 mm. The hot rolled sheetis subjected to normalization annealing at 1000° C. and cold rolledtwice through an intermediate annealing at 1050° C. to obtain a finalcold rolled sheet of thickness: 0.23 mm.

After the decarburization and primary recrystallization annealing in wetH₂ of 840° C., a slurry of an annealing separator having a compositionof CaO(10%), Al₂O₃(50%) and SiO₂(40%) is applied to the surface of thesteel sheet and annealed at 850° C. for 15 hours and temperature israised from 850° C. to 1100° C. at a rate of 12° C./h to developsecondary recrystallized grains strongly aligned in Goss orientation andsubjected to purification annealing in dry H₂ of 1200° C.

The thus obtained silicon steel sheet having no forsterite base film issubjected to a pickling treatment in an aqueous solution of SiCl₄: 50 ccdissolved in 1500 cc of a distilled water at 80° C. for 60 seconds toremove the oxide from the surface and treated in a mixed gas ofN₂(50%)+H₂(50%) at 950° C. for 5 minutes.

Thereafter, it is immersed in a treating solution (80° C.) obtained bydiluting 250 cc of a coating solution for tension insulating filmconsisting essentially of magnesium phosphate and colloidal silica with1500 cc of a distilled water and adding SiCl₄: 20 cc, AlPO₄: 10 g andH₃BO₄: 10 g to the diluted solution for 20 seconds and treated in amixed gas of N₂(93%)+H₂(7%) at 950° C. for 5 minutes to form abase filmhaving a thickness: 0.3 μm.

Thereafter, a coating solution for tension insulating film consistingessentially of colloidal silica and magnesium phosphate is coated on thesurface of the steel sheet, dried and baked at 800° C. to form a tensioninsulating film having a thickness: about 2 μm.

The magnetic properties, adhesion property and magnetostriction propertyin the thus obtained product are as follows.

Magnetic properties B₈: 1.94 T W_(17/50): 0.62 W/kg Adhesion propertygood without peeling by 180° bending on a round rod of diameter: 20 mmMagnetostriction magnetic strain λ_(pp) = 0.7 × 10⁻⁶ at compressionstress σ = 0.4 kg/mm², magnetic strain λ_(pp) = 1.2 × 10⁻⁶ atcompression stress σ = 0.6 kg/mm²

EXAMPLE 16

A continuously cast slab of silicon steel having a composition of C:0.077 wt %, Si: 3.46 wt %, Mn: 0.070 wt %, Se: 0.019 wt %, Sb: 0.025 wt%, Al: 0.020 wt %, N: 0.0074 wt % and Mo: 0.013 wt % and the remainderbeing substantially Fe is heated at 1350° C. for 5 hours and hot rolledto obtain a hot rolled sheet of thickness: 2.0 mm. The hot rolled sheetis subjected to normalization annealing at 1000° C. and cold rolledtwice through an intermediate annealing at 1030° C. to obtain a finalcold rolled sheet of thickness: 0.23 mm.

Then, an etching resist ink consisting essentially of an alkyd resin isapplied onto the surface of the final cold rolled sheet by gravureoffset printing so as to leave linear non-coated portions of width: 200μm at an interval: 4 mm in a direction substantially perpendicular to arolling direction, and baked at 200° C. for about 20 seconds. In thiscase, a resist thickness is 2 μm. The steel sheet coated with theetching resist is subjected to an electrolytic etching to form lineargrooves of width: 200 μm and depth: 20 μm and then immersed in anorganic solvent to remove the resist. In this case, the electrolyticetching is carried out in NaCl electrolyte under conditions of currentdensity: 10 A/dm² and treating time: 20 seconds.

After the decarburization and primary recrystallization annealing in wetH₂ of 850° C., a slurry of an annealing separator having a compositionof MgO(5%), CaO(25%), Al₂O₃(30%), CaSiO₃(10%) and SiO₂(30%) is appliedto the surface of the steel sheet and annealed at 850° C. for 15 hoursand temperature is raised from 850° C. to 1050° C. at a rate of 12° C./hto develop secondary recrystallized grains strongly aligned in Gossorientation and subjected to purification annealing in dry H₂ of 1220°C.

The surface of the thus obtained silicon steel sheet having noforsterite film is treated under the following two conditions.

{circle around (1)} It is immersed in an aqueous solution of SiCl₄: 45cc and FeCl₃: 10 g dissolved in 1500 cc of a distilled water at 85° C.for 60 seconds.

{circle around (2)} After the treatment of the item {circle around (1)},the surface of the steel sheet is further subjected to chemicalpolishing with a mixed solution of (3%HF+97%H₂O₂).

Then, each of the steel sheets is immersed in an aqueous solution ofSiCl₄: 20 cc dissolved in 1500 cc of a distilled water at 80° C. for 20seconds and subjected to a heat treatment in a mixed gas ofN₂(50%)+H₂(50%) at 950° C.

Thereafter, a coating solution for tension insulating film consistingessentially of colloidal silica and magnesium phosphate is coated on thesurface of the steel sheet, dried and baked at 800° C. to form a tensioninsulating film having a thickness: about 1.5 μm.

The magnetic properties and adhesion property in the thus obtainedproduct are as follows. Silicon steel sheet treated under the condition{circle around (1)}

Magnetic properties B₈: 1.91 T W_(17/50): 0.62 W/kg Adhesion propertygood without peeling by 180° bending on a round rod of diameter: 20 mm

Silicon steel sheet treated under the condition {circle around (1)}

Magnetic properties B₈: 1.91 T W_(17/50): 0.57 W/kg Adhesion propertygood without peeling by 180° bending on a round rod of diameter: 20 mm

EXAMPLE 17

A continuously cast slab of silicon steel having a composition of C:0.044 wt %, Si: 3.37 wt %, Mn: 0.069 wt %, Se: 0.021 wt %, Sb: 0.024 wt% and Mo: 0.012 wt % and the remainder being substantially Fe is heatedat 1320° C. for 4 hours and hot rolled to obtain a hot rolled sheet ofthickness: 2.4 mm. The hot rolled sheet is subjected to normalizationannealing at 950° C. and cold rolled twice through an intermediateannealing at 1000° C. to obtain a final cold rolled sheet of thickness:0.23 mm.

Then, an etching resist ink consisting essentially of an alkyd resin isapplied onto the surface of the final cold rolled sheet by gravureoffset printing so as to leave linear non-coated portions of width: 200μm at an interval: 4 mm in a direction substantially perpendicular to arolling direction, and baked at 200° C. for about 20 seconds. In thiscase, a resist thickness is 2 μm. The steel sheet coated with theetching resist is subjected to an electrolytic etching to form lineargrooves of width: 200 μm and depth: 20 μm and then immersed in anorganic solvent to remove the resist. In this case, the electrolyticetching is carried out in NaCl electrolyte under conditions of currentdensity: 10 A/dm² and treating time: 20 seconds.

After the decarburization and primary recrystallization annealing in wetH₂ of 840° C., a slurry of an annealing separator having a compositionof MgO(5%), Al₂O₃(50%), CaSiO₃(15%) and SiO₂(30%) is applied to thesurface of the steel sheet and subjected to temperature-holdingannealing at 850° C. for 50 hours to develop secondary recrystallizedgrains strongly aligned in Goss orientation and subjected topurification annealing in dry H₂ of 1220° C.

The thus obtained silicon steel sheet having no forsterite film isimmersed in an aqueous solution of SiCl₄: 55 cc dissolved in 1500 cc ofa distilled water at 85° C. for 60 seconds. Thereafter, the siliconsteel sheet is further immersed in an aqueous solution of SiCl₄: 15 ccdissolved in 1500 cc of a distilled water at 90° C. for 15 seconds andtreated in a mixed gas of N₂(50%)+H₂(50%) at 900° C.

Thereafter, it is immersed in a treating solution (80° C.) obtained bydiluting 200 cc of a coating solution for tension insulating filmconsisting essentially of aluminum phosphate and colloidal silica with2000 cc of a distilled water and adding SiCl₄: 20 cc to the dilutedsolution for 40 seconds and subjected to a heat treatment in a mixed gasof N₂(93%)+H₂(7%) at 950° C. for 3 minutes to form a base film having athickness: 0.4 μm.

Thereafter, a coating solution for tension insulating film consistingessentially of colloidal silica and aluminum phosphate is coated on thesurface of the steel sheet, dried and baked at 800° C. to form a tensioninsulating film having a thickness: about 2.5 μm.

The magnetic properties and adhesion property in the thus obtainedproduct are as follows.

Magnetic properties B₈: 1.88 T W_(17/50): 0.65 W/kg Adhesion propertygood without peeling by 180° bending on a round rod of diameter: 20 mm

After the above product is subjected to a strain relief annealing at800° C. for 3 hours, the magnetic properties are examined to obtainresults as follows:

Magnetic properties B₈: 1.88 T W_(17/50): 0.64 W/kg

EXAMPLE 18

A continuously cast slab of silicon steel having a composition of C:0.073 wt %, Si: 3.42 wt %, Mn: 0.076 wt %, Se: 0.020 wt %, Sb: 0.025 wt%, Al: 0.020 wt %, N: 0.0074 wt % and Mo: 0.012 wt % and the remainderbeing substantially Fe is heated at 1340° C. for 5 hours and hot rolledto obtain a hot rolled sheet of thickness: 2.0 mm. The hot rolled sheetis subjected to normalization annealing at 1000° C. and cold rolledtwice through an intermediate annealing at 1030° C. to obtain a finalcold rolled sheet of thickness: 0.23 mm.

Then, an etching resist ink consisting essentially of an alkyd resin isapplied onto the surface of the final cold rolled sheet by gravureoffset printing so as to leave linear non-coated portions of width: 200μm at an interval: 4 mm in a direction substantially perpendicular to arolling direction, and baked at 200° C. for about 20 seconds. In thiscase, a resist thickness is 2 μm. The steel sheet coated with theetching resist is subjected to an electrolytic etching to form lineargrooves of width: 200 μm and depth: 20 μm and then immersed in anorganic solvent to remove the resist. In this case, the electrolyticetching is carried out in NaCl electrolyte under conditions of currentdensity: 10 A/dm² and treating time: 20 seconds.

After the decarburization and primary recrystallization annealing in wetH₂ of 850° C., a slurry of an annealing separator having a compositionof MgO(5%), CaO(25%), Al₂O₃(30%), CaSiO₃(10%), SiO₂(20%) and PbCl₂(20%)is applied to the surface of the steel sheet and annealed at 850° C. for15 hours and temperature is raised from 850° C. to 1050° C. at a rate of12° C./h to develop secondary recrystallized grains strongly aligned inGoss orientation and subjected to purification annealing in dry H₂ of1220° C.

The surface of the thus obtained silicon steel sheet having noforsterite film is treated under the following two conditions.

{circle around (1)} It is immersed in an aqueous solution of HCl: 25 cc,H₃PO₄: 25 cc and SiCl₄: 45 cc dissolved in 1500 cc of a distilled waterat 85° C. for 60 seconds.

{circle around (2)} After the treatment of the item {circle around (1)},the surface of the steel sheet is further subjected to chemicalpolishing with a mixed solution of (3%HF+97%H₂O₂).

Then, each of the steel sheets is immersed in an aqueous solution ofSiCl₄: 20 cc dissolved in 1500 cc of a distilled water at 80° C. for 20seconds.

Thereafter, it is immersed in a treating solution (80° C.) obtained byadding SiCl₄: 25 cc, AlCl₃: 5 g and H₃BO₄: 10 g to a diluted solutionobtained by dissolving 250 cc of a coating solution for tensioninsulating film consisting essentially of magnesium phosphate andcolloidal silica in 1500 cc of a distilled water for 20 seconds to froma base film having a thickness: 0.3 μm.

Thereafter, a coating solution for insulating film consistingessentially of magnesium phosphate and chromic acid is applied onto thesurface of the steel sheet at a thickness of 0.5 μm and then a coatingsolution for tension insulating film consisting essentially of colloidalsilica and magnesium phosphate is coated thereon, dried and baked at800° C. to form a tension insulating film having a thickness: about 1.0μm.

The magnetic properties and adhesion property in the thus obtainedproduct are as follows.

Silicon steel sheet treated under the condition {circle around (1)}

Magnetic properties B₈: 1.91 T W_(17/50): 0.65 W/kg Adhesion propertygood without peeling by 180° bending on a round rod of diameter: 20 mm

Silicon steel sheet treated under the condition {circle around (2)}

Magnetic properties B₈: 1.91 T W_(17/50): 0.62 W/kg Adhesion propertygood without peeling by 180° bending on a round rod of diameter: 20 mm

EXAMPLE 19

A continuously cast slab of silicon steel having a composition of C:0.076 wt %, Si: 3.32 wt %, Mn: 0.071 wt %, Se: 0.020 wt %, Sb: 0.025 wt%, Al: 0.020 wt %, N: 0.0068 wt % and Mo: 0.012 wt % and the remainderbeing substantially Fe is heated at 1350° C. for 4 hours and hot rolledto obtain a hot rolled sheet of thickness: 2.0 mm. The hot rolled sheetis subjected to normalization annealing at 1000° C. and cold rolledtwice through an intermediate annealing at 1050° C. to obtain a finalcold rolled sheet of thickness: 0.23 mm.

Then, an etching resist ink consisting essentially of an alkyd resin isapplied onto the surface of the final cold rolled sheet by gravureoffset printing so as to leave linear non-coated portions of width: 200μm at an interval: 4 mm in a direction substantially perpendicular to arolling direction, and baked at 200° C. for about 20 seconds. In thiscase, a resist thickness is 2 μm. The steel sheet coated with theetching resist is subjected to an electrolytic etching to form lineargrooves of width: 200 μm and depth: 20 μm and then immersed in anorganic solvent to remove the resist. In this case, the electrolyticetching is carried out in NaCl electrolyte under conditions of currentdensity: 10 A/dm² and treating time: 20 seconds.

After the decarburization and primary recrystallization annealing in wetH₂ of 840° C., a slurry of an annealing separator having a compositionof MgO(5%), CaO(25%), Al₂O₃(30%), CaSiO₃(10%), SiO₂(20%) and PbCl₂(10%)is applied to the surface of the steel sheet and annealed at 850° C. for15 hours and temperature is raised from 850° C. to 1080° C. at a rate of12° C./h to develop secondary recrystallized grains strongly aligned inGoss orientation and subjected to purification annealing in dry H₂ of1220° C.

The thus obtained silicon steel sheet is immersed in an aqueous solutionof HCl: 30 cc, H₃PO₄: 25 cc and SiCl₄: 25 cc dissolved in 1500 cc of adistilled water at 85° C. for 60 seconds. Thereafter, the surface of thesteel sheet is further subjected to chemical polishing in a mixedsolution of (3%HF+97%H₂O₂).

Then, the silicon steel sheet is treated in a vacuum glow box in N₂atmosphere as follows.

That is, the silicon steel sheet is immersed in an aqueous solution ofSiCl₄: 20 cc dissolved in 1500 cc of a distilled water at 90° C. for 10seconds and then exposed in N₂ atmosphere for 5 seconds. This treatmentis repeated three times.

Thereafter, it is immersed in a treating solution (80° C.) obtained bydiluting 250 cc of a coating solution for tension insulating filmconsisting essentially of magnesium phosphate and colloidal silica with1500 cc of a distilled water and adding SiCl₄: 25 cc, AlCl₃: 5 g andH₃BO₄: 10 g to the diluted solution for 20 seconds to form a base filmhaving a thickness: 0.3 μm.

Thereafter, a coating solution for insulating film consistingessentially of magnesium phosphate and chromic acid is applied onto thesurface of the steel sheet at a thickness of 0.5 μm and then a coatingsolution for tension insulating film consisting essentially of colloidalsilica and magnesium phosphate is coated thereon, dried and baked at800° C. to form a tension insulating film having a thickness: about 1.0μm.

The magnetic properties and adhesion property in the thus obtainedproduct are as follows.

Magnetic properties B₈: 1.91 T W_(17/50): 0.62 W/kg Adhesion propertygood without peeling by 180° bending on a round rod of diameter: 20 mm

INDUSTRIAL APPLICABILITY

According to the invention, the interface layer including nitride-oxideof one or more selected from Fe, Si, Al and B is formed at the interfacebetween the matrix surface and the tension insulating film in thesilicon steel sheet, whereby the core loss can considerably be reducedand also the compression stress property of magnetostriction caneffectively be improved and further the improvement of productionefficiency and the decrease of cost can be attained.

What is claimed is:
 1. An ultra-low core loss grain oriented siliconsteel sheet having a matrix surface and having on said matrix surface atension insulating film consisting essentially of a phosphate andcolloidal silica, said sheet having a thickness of 0.05˜0.5 mm afterfinal annealing, and said sheet having an interface layer comprising oneor more nitride-oxides selected from the group consisting of Fe, Si, Aland B positioned between said matrix surface of the steel sheet and saidtension insulating film.
 2. An ultra-low core loss grain orientedsilicon steel sheet according to claim 1, wherein said interface layeris a Si-containing nitride-oxide layer having a thickness of about0.00-3.0 μm.
 3. An ultra-low core loss grain oriented silicon steelsheet according to claim 1, wherein said interface layer is a base filmcomprising one or more nitride-oxides selected from the group consistingof Fe, Si, Al and B said group being combined with the same filmcomponents as said tension insulating film.
 4. An ultra-low core lossgrain oriented silicon steel sheet according to claim 1 wherein saidmatrix surface of said steel sheet is provided with linear concaveregions having a width of 50˜500 μm and a depth of 0.1˜50 μm at aninterval of 2˜10 mm in a direction to a transverse rolling direction ofsaid sheet.
 5. An ultra-low core loss grain oriented silicon steel sheetaccording to any of claims 1-4 wherein the surface of the grain orientedsilicon steel sheet after final annealing is further subjected to asmoothening treatment.
 6. An ultra-low core loss grain oriented siliconsteel sheet according to any of claims 1-4, wherein the surface of thegrain oriented silicon steel sheet is subjected to pickling but is notsubjected to a smoothening treatment.
 7. An ultra-low core loss grainoriented silicon steel sheet according to claim 1, wherein the interfacelayer is an extremely thin Si-containing nitride-oxide layer, whereinthe matrix surface of the steel sheet is provided with linear concaveregions having a width: 50˜500 μm and a depth: 0.1˜50 μm at an intervalof 2˜10 mm in a direction crossing its rolling direction.
 8. Anultra-low core loss grain oriented silicon steel sheet according toclaim 1, wherein the interface layer is an extremely thin base filmformed by finely dispersing nitride-oxide of one or more selected fromFe, Si, Al and B into the same film components as the tension insulatingfilm, wherein the matrix surface of the steel sheet is provided withlinear concave regions having a width: 50˜500 μm and a depth: 0.1˜50 μmat an interval of 2˜10 mm in a direction crossing its rolling direction.9. An ultra-low core loss grain oriented silicon steel sheet having arolling direction, having a matrix surface and having on said matrixsurface a tension insulating film consisting essentially of a phosphateand colloidal silica and having a thickness of 0.05˜0.5 mm after finalannealing, wherein an interface layer comprising one or morenitride-oxides selected from the group consisting of Fe, Si, Al, and Bpositioned between said matrix surface of the steel sheet and saidtension insulating film, wherein said matrix surface of the steel sheetis provided with linear concave regions having a width: 50˜500 μm and adepth: 0.1˜50 μm at an interval of 2˜10 mm in a direction crossing itsrolling directions.